n.

1. （兽的）臀部；（鸟的）尾部；（人的）臀部[C]
   He sent the horse forward with a slap on its rump.

   他拍了一下马尾，马便向前跑去。

2. 牛臀肉[U]
3. 残余部分；渣滓[C][the S]
4. 余党[C][the S]

n.

1. the hind part of the body of a mammal or the lower back of a bird.
   ▸chiefly humorous a person's buttocks.
2. a small or unimportant remnant.