Rear is defined as the back of something.(noun)
An example of rear is the backseat of a car.
The definition of rear is relating to the back of something.(adjective)
An example of rear used as an adjective is rear window which means the window in the back of a car.
See rear in Webster's New World College Dictionary
Origin: prob. back-form. < rear(ward), rear (guard)
Origin: ME reren < OE ræran, caus. of risan, to rise
See rear in American Heritage Dictionary 4
Origin: Middle English rere, rear of an army
Origin: , short for rerewarde, rear guard; see rearward2.
verb reared, rear·ing, rears verb, transitive
Origin: Middle English reren, to raise
Origin: , from Old English rǣran; see er-1 in Indo-European roots.
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