dead horse
Literal meaning: a horse that has died. Can be used in proverbial or figurative contexts.
A dead horse was lying by the roadside.
stupid horse; useless horse; crowbait
Derogatory term for a horse that is considered worthless or incompetent. Often used in insults or complaints about a horse's performance.
That useless horse came in last again in the race.
It's a waste to feed a crowbait like this.
Compound of 死に (stem of 死ぬ 'to die') + 馬 'horse'. The literal meaning is 'dead horse', and the derogatory sense extends from the idea of a horse so useless it might as well be dead.