rear end
1. noun Literally, the rear-most part of something. There is a dining car at the rear end of the train.
2. noun By extension, a euphemism for the buttocks. Does my rear end look big in these pants?
3. verb To hit another car from behind with one's own. Usually hyphenated. The other driver was definitely at fault—I was just sitting at a red light when he rear-ended me!
rear end
1. The back part of anything, especially a vehicle, as in There's a large dent in the rear end of the car.
2. The buttocks, as in I'm afraid these pants don't fit my rear end. The noun rear alone has been used in both these senses, the first since the late 1700s and the second since the mid-1900s. The addition of end occurred in the first half of the 1900s.
rear (end)
n. the tail end; the buttocks. (Euphemistic.) The dog bit her in the rear end.