1. A toy horse, usually comprised of a figure of a horse's head attached to a stick.
2. A toy horse that, via various mechanics, stimulate the riding of a horse through rocking.
(Etymology I- Derived possibly from the "'Obby 'Oss", an English folk tradition wherein Morris Dancers dress as horses, which, in itself, is probably derived from the IRISH HOBBY, a breed of horse, now extinct, that the "'Obby 'Oss" was probably made to resemble)
1. A favourite topic.
(Possibly from Lawrence Sterne's "Tristram Shandy", who uses it, quite frequently, in the third sense)
1. A female of loose virtue and even looser undergarments, a woman who is 'easy to get', a lady who uses sex as a means of earning legal tender. See Prostitute, loose woman, and strumpet.
(Derived from def. I, 'a toy horse', she can be 'ridden' by all)
"And Yung Matthais riden oot to Banbery Cross atop his Hobbi-Horse sted..."
John of Ingelwit, 1503
"Almost every person hath some Hobby Horse or other wherein he prides himself"
Sir Matthew Hale-1676
"Nay, if you come to that, Sir, have not the wisest of men in all ages, not excepting Solomon himself- have they not their Hobby Horses..."