Noun
A strong, active horse, of a middle size, said to have been originally from Ireland; an ambling nag.
A stick, often with the head or figure of a horse, on which boys make believe to ride.
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.
Source: Webster's dictionarydon't get him started on his hobbyhorse Source: Internet
Another theory says that the name "Dada" came during a meeting of the group when a paper knife stuck into a French-German dictionary happened to point to 'dada', a French word for 'hobbyhorse'. Source: Internet
The choice of topic was chosen less from Grierson's curiosity than the fact that he discovered that the Financial Secretary had made the herring industry his hobbyhorse. Source: Internet