The definition of behind means in back, toward the rear, in a former place or late.(adverb)
Behind means the buttocks.(noun)
An example of a behind is the rear end.
Behind is the back of something or later than.(preposition)
See behind in Webster's New World College Dictionary
Origin: ME bihinden < OE behindan: see be- & hind
See behind in American Heritage Dictionary 4
Origin: Middle English bihinde
Origin: , from Old English behindan; see ko- in Indo-European roots.
Learn more about behind