hobby

from The Century Dictionary.

• noun A small European falcon of the genus Falco and subgenus Hypotriorchis, H subbuteo.
• noun A strong active horse of medium size having an ambling gait; a pacing horse; a nag; a garran.
• noun Same as hobby-horse, 3.
• noun Any favorite object, pursuit, or topic; that which a person persistently pursues or dwells upon with zeal or delight, as if riding a horse.
• noun A goose.
• noun A stupid fellow.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A small, strong-winged European falcon (Falco subbuteo), formerly trained for hawking.
• noun A strong, active horse, of a middle size, said to have been originally from Ireland; an ambling nag.
• noun A stick, often with the head or figure of a horse, on which boys make believe to ride.
• noun A subject or plan upon which one is constantly setting off; a favorite and ever-recurring theme of discourse, thought, or effort; that which occupies one's attention unduly, or to the weariness of others; a ruling passion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any of four species of small falcons in the genus Falco, especially Falco subbuteo.
• noun An activity that one enjoys doing in one's spare time.
• noun horses An extinct breed of horse native to the British Isles, also known as the Irish Hobby

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an auxiliary activity
• noun small Old World falcon formerly trained and flown at small birds
• noun a child's plaything consisting of an imitation horse mounted on rockers; the child straddles it and pretends to ride