noun
cart-horse; workhorse
Refers literally to a horse that pulls a cart or carriage. Often used figuratively for a person who works tirelessly.
昔は馬車馬が荷物を運んでいた。
In the past, cart-horses carried goods.
noun
wholeheartedly; with undivided attention
Used in the pattern 馬車馬のように to describe working single-mindedly and tirelessly, like a cart-horse.
彼は馬車馬のように働いている。
He works like a horse.