"Hypocorism" explained

I encountered the word in a crossword puzzle clue.  As an almost-eighty-year-old English major, I still learn something every day...

Hypocorism: A term of endearment, often a diminutive; a pet name; a nickname.  Rarely used for "baby talk", such as bow-wow for dog and choo-choo for train. 

"Hypocorism joined the English language in the mid-19th century and was once briefly a buzzword among linguists, who used it rather broadly to mean "adult baby talk"—that is, the altered speech adults use when supposedly imitating babies. Once the baby talk issue faded, hypocorism settled back into being just a fancy word for a pet name. Pet names can be diminutives like "Johnny" for "John," endearing terms such as "honey-bunch," or, yes, names from baby talk, like "Nana" for "Grandma."

Etymology from Greek terms for "a small degree" + "caress".