hobby horse

Noun

• The Irish hobby, an extinct breed of horse.
• A child's toy consisting of a (usually wooden or cloth) horse's head mounted on a stick.
• A topic about which someone loves to talk at great length.
• A puppet-like costume used in some traditional dances and festivals that gives its wearer the appearance of a man on horseback.
• An early bicycle with no pedals or brakes; a draisienne.