This was one of the first books I received after joining a book club in the 1960s. This winter I gave it a final goodbye-read and while doing so made a list of interesting words. Most of the definitions below are from Wiktionary.
"kith not kin" Friends and acquaintances, as opposed to relatives. From a Middle English word meaning "kinsman."
"... young Stamford, who had been a dresser under me at Bart's." A wardrobe assistant (at St. Bartholomew's Hospital) - but why would Watson have needed a dresser?
"... Lauriston Gardens wore an ill-omened and minatory look." Threatening (from a Middle French word cognate to "menacing.")
"... foxhound, as it dashes backward and forward through the covert..." Familar as an adjective; unusual to see it used as a noun (here "undergrowth" rather than "hiding place.")
"... if a man can stride four and a half feet without the smallest effort, he can't be quite in the sere and yellow." A phrase used in Macbeth: "I have liv'd long enough: my way of life/Is fall'n into the sear, the yellow leaf;/And that which should accompany old age." Sere meaning dried up, worn thin, aged or infirm.
"... the unemotional Indians, journeying in with their peltries..." Plural of "pelt" (skin with fur still attached)/
"The ordinary London growler is considerably less wide than a gentleman's brougham." A horse-drawn cab with four wheels. ?onomatopoeia?
"... Jefferson Hope was to be found among the jarveys of the Metropolis." The driver of a hackney coach, probably named after a saint (Gervais) or a person.
"I am compelled to be a valetudinarian." A sickly person or one overly worried about his health.
"... the great rubbish-heaps which cumbered the grounds." Uncommon to see it without the "en-" prefix.
"Window is snibbed on the inner side." Latched (Scottish or Australian term)
"Don't mind that, sir; it's only a slowworm. It hain't got no fangs..." A legless lizard often mistaken for a snake.
"... half spaniel and half lurcher..." A crossbreed between a sighthound and some other breed.
"... drinking whiskey-pegs and smoking cheroots..." [I need help with this one]
"... with his pockets full of gold moidores." Portuguese gold coins ("moeda de ouro")
"... a spirit case and a gasogene in the corner." A Victorian seltzer bottle.
"Was the photograph a cabinet?" A photo measuring 3⅞" by 5½
"It was the bisulphate of baryta." A barium compound.
"... playing backgammon and draughts with me..." Checkers.
"... the rascally lascar who runs it..." A sailor, army servant or artilleryman from India or Southeast Asia.
"A dull wrack was drifting slowly across the sky..." Apparently high clouds.
"... to avoid the police regulations he pretends to a small trade in wax vestas." A short match
"I should be compelled to stop the night." "Yes, we could easily give you a shake-down." In this sense, a place to sleep ("An improvised bed would originally have been made by shaking down straw").
"Circumstantial evidence is occasionally very convincing, as when you find a trout in the milk, to quote Thoreau's example."
"... he tried to bluster and took down a life-preserver from the wall." A gun in context, but could also be a weighted club.
"... his stick, which was a penang-lawyer weighted with lead, was just such a weapon..." A kind of walking stick made from the stem of an East Asiatic palm. Etymology: perhaps a corruption of Penang liyar, the wild areca.
"... dark-haired, dark-eyed, black-bearded man, with a touch of the sheeny about his nose." Jew (etymology unknown).
"... a barrel of water, two casks, one of junk and one of biscuits, and a compass." In a nautical setting, junk would be salt beef.
"It's a mongoose," I cried." "Well, some call them that, and some call them ichneumon..." The Latin term for mongoose, meaning "tracker." ?
"It ended in my moving into the house next Lady Day..." March 25 is an English quarter day (day that starts a quarter year)
"She explained that she was the commissionaire's wife, who did the charing, and I gave her the order for the coffee." Housework (related to chore).
"... taking off their boots at the commissionaire's office, and putting on list slippers." "Slippers made from cloth whose edge has a border that keeps it the cloth from unraveling."
"At last the violet rim of the German Ocean appeared over the green edge of the Norfolk coast..." North Sea.
"The first who entered was a little Ribston pippin of a man..." "A triploid cultivar of winter apple with firm flesh and a yellow skin streaked with red." Pippin from ME "seed."
"... he is a plethoric sleeper." Ruddy, congested
"The top steps swilled down and the other ones dry." Washed by flooding with water. Related to English swallow.
"Holmes was curiously distrait..." Absent minded, but in this case distracted. From the French.
"... I've skippered the 'Varsity all this year." Has an apostrophe because it is a shortening of "University" !! You learn something every day.
"This carpet was a small square drugget in the centre of the room..." Inexpensive coarse woolen cloth, from French drogue ("cheap")
"I tell you, Watson, this time we have got a foeman who is worthy of our steel." Another term for "foe," seems archaic (comes direct from Middle English).
"... a wagonette with a pair of cobs was waiting." The context allows us to rule out swans, corncobs, a loaf of bread, Spanish coins, and spiders, so he apparently was referring to "horses having a stout body and short legs."
"... heavily raftered with huge baulks of age-blackened oak." Beam, crossbeam; squared timber; a tie beam of a house, stretching from wall to wall, especially when laid so as to form a loft, "the balks". Again, directly from Middle English.
"You are developing a certain unexpected vein of pawky humour, Watson..." Shrewd, sly - apparently related to "Puck."
"... emerge with your year's pension as a solatium for his wounded character." "A form of compensation for emotional rather than physical or financial harm." Sounds like it should be related to "consolation."
"... Hugo de Capus built a fortalice in the centre of the estate..." A small fortress (Latin fortalitia).
"You seem heeled and ready." Prepared (archaic). Etymology??
"It is late in March, so quarter-day is at hand." (see Lady Day, above).
"... leaning back in my chair, I fell into a brown study." I always chuckle at this phrase. A state of mental abstraction; purposeless reverie (from brown in sense of gloomy).
"... with large, gentle eyes, and grizzled hair curving down over her temples..." Mixed with gray, from the French gris.
"... he held out his hands quietly enough for the darbies." Handcuffs, manacles (Br. slang)
"Mr. Warren is a timekeeper at Morton and Waylight's..." The meaning is clear, but the reason for the occupation is obscure to me.
"Those hectic spots were more pronounced, the eyes shone more brightly out of darker hollows..." Referring to a flushed (reddened) skin.
"Old Susan Dobney with the mob cap! I remember her well." A plain cap or headdress for women or girls, especially one tied under the chin by a very broad band.
"It was a large and bright dwelling, rather a villa than a cottage..." A house often larger and more expensive than average, or a semi-detached family house in a middle-class street.
"According to his lights he has been a kind master." A person's ideas, knowledge, or understanding.
"His lucent top-hat, his dark frock-coat..." In this sense must be "shining" rather than "transparent."
"... gave a hurried order to the cockaded coachman..." Wearing a rosette or knot of ribbon worn in a hat, especially as an office or party badge. (from the French)
"The ideas of my friend Watson, though limited, are exceedingly pertinacious." Holding tenaciously to a position; persistent
"We had a bit of barney right away..." Lots of meanings, typically in the sense of a lark, a hoax, a humbug, or an argument, or a minor physical fight. Context needed.
"He is a great big silly bull-headed gudgeon. But he is flopping about in my net all the same." A freshwater fish (also used to denote an idiot, so perhaps a double entendre here).
"He's a leary cove that wants watching." Alternative spelling of "leery." Cove = fellow, friend, mate.
"... has made some inquiry from us in a communication of even date concerning vampires." Having the same date.
"... the execrations which so many business rivals have heaped upon his head." Curses.
"... a boxer, an athlete, a plunger on the turf, a lover of fair ladies, and, by all accounts, so far down Queer Street that he may never find his way back again." Hard times, especially financially (etymology unknown).
"In the morning I was up betimes..." In good time (by-time).
"The old colourman had the strength of a lion in that great trunk of his..." In context doesn't make sense as a person who sells paints, or a commentator in a sporting event. Perhaps refers to wearing of colors of some military unit??
Addendum: As always when I blog material like this, I offer a big tip of the blogging cap to readers here, who have filled the Comments section with new viewpoints and lots of clarifying and correcting information.