ˈ ̷ ̷ˌ ̷ ̷ noun
1.
a. : a horse that in a hitch of four or more horses pulls a vehicle in a position nearest the front wheels
b. : a horse that is a strong and willing worker
2. : a steady and effective worker or adherent especially in a political party or body
had been a useful wheelhorse pushing through legislation desired by the administration — R.D.Leigh
the day-to-day work of the union is carried on by a few wheelhorses who are willing to put in the necessary time — L.G.Reynolds