|Origin:||hobby 'small horse' (14-19 centuries) (probably from Hobbin, a man's name, from Robin) + horse|
a subject that someone has strong opinions about and that they talk about too much:
I'm afraid safe driving isn't Jaqui's only hobbyhorse.
be on your hobbyhorse
Vicky was on her hobbyhorse again.
an old-fashioned toy made of a horse's head on a stick