work·horse 
(wûrkhôrs′)
(wûrkhôrs′)n.
1. Something, such as a machine, that performs dependably under heavy or prolonged use: "the 50-year-old DC-3 ... one of aviation's most effective workhorses" (Christian Science Monitor).
2. A horse that is used for labor rather than for racing or riding.
3. Informal A person who works tirelessly, especially at difficult or time-consuming tasks.
- out of one's head
- out of phase
- out of play
- out of plumb
- out-of-pocket
- out of pocket
- out of print
- out of season
- out of sight
- out of sorts
- out of square
- out-of-state
- out-of-stater
- out of step
- out of stock
- out of the blocks
- out of the blue
- out of the chute
- out of the loop
- out of the question
- out of the running
- out-of-the-way
- out of the way
- out of the woods
- out of the woodwork