HOBBY, a small horse, probably from early quotations, of Irish breed, trained to an easy gait so that riding was not fatiguing. The common use of the word is for a favourite pursuit or occupation, with the idea either of excessive devotion or of absence of ulterior motive or of profit, etc., outside the occupation itself. This use is probably not derived from the easy ambling gait of the Irish " hobby," but from the " hobby-horse," the mock horse of the old morris-dances, made of a painted wooden horse's head and tail, with a framework casing for an actor's body, his legs being covered by a cloth made to represent the " housings " of the medieval tilting-horse. A hobby or hobbyhorse is thus a toy, a diversion. The O. Fr. hobin, or 1/obi, Mod. aubin, and Ital. ubina are probably adaptations of the English, according to the New English Dictionary. The O. Fr. hober, to move, which is often taken to be the origin of all these words, is the source of a use of " hobby " for a small kind of falcon, falco subbuteo, used in hawking.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)