"The word hart is an old alternative word for "stag" (from Old English heorot, "deer" – compare with modern Dutch hert and Swedish/Norwegian hjort, also "deer").Posted for the Hartshorns, and for people who know people named Hartshorn.
Specifically, the word "hart" was used of a red deer stag more than five years old. In medieval hunting terms, a stag in its first year was called a "calf" or "calfe", in its second a "brocket", in its third a "spayed", "spade", or "spayard", in its fourth a "staggerd" or "staggard", and in its fifth a "stag", or a "great stag". To be a "hart" was its fully mature state. A lord would want to hunt not just any deer, but a mature stag in good condition, partly for the extra meat and fat it would carry, but also for prestige. Hence a hart could be designated "a hart of grease", (a fat stag), "a hart of ten", (a stag with ten points on its antlers) or "a royal hart" (a stag which had been hunted by a royal personage). A stag which was old enough to be hunted was called a "warrantable" stag.
The hart was a "beast of venery" representing the most prestigious form of hunting, as distinct from lesser "beasts of the chase", and "beasts of warren", the last of which were considered virtually as being vermin. The membership of these different classes varies somewhat, according to which period, and which writer, is being considered, but the red deer is always in the first class, the fox hardly being regarded at all.
Harts' horns, are the horns of the male red deer. Various substances were made from the shavings of the animals' horns. The oil of hartshorn is a crude animal oil obtained from the destructive distillation of the deers' bones or horns.
The salt of hartshorn actually refers to two distinct substances, sal ammoniac (ammonium chloride), and ammonium carbonate, which have been obtained from oil of hartshorn by dry distillation. The spirit of hartshorn (or spirits of hartshorn) is an aqueous solution of ammonia...
Hartshorn jelly or a decoction of burnt hartshorn in water was used to treat diarrhea. Hartshorn was used to treat insect bites, sunstroke, stye, and snakebites.
Hartshorn salt (ammonium carbonate), also known simply as hartshorn, and baker's ammonia, was used as a leavening agent, in the baking of cookies and other edible treats. It was used mainly in the 17th and 18th centuries as a forerunner of baking powder. ½ teaspoon of hartshorn can substitute for 1 teaspoon of baking powder. It is called for in old German and Scandinavian recipes and, though rarely used in modern times, may still be purchased as a baking ingredient."