WordNet sense 1 (a child's plaything consisting of an imitation horse mounted on rockers; the child straddles it and pretends to ride):

hobbyhorse, rocking horse

WordNet sense 2 (small Old World falcon formerly trained and flown at small birds):

Falco subbuteo

WordNet sense 3 (an auxiliary activity):

avocation, pursuit, sideline, by-line, spare-time activity