Definition of behind :
1. After the departure of another; as, to stay behind.
2. At the back part; in the rear.
3. Backward in time or order of succession; past.
4. Left a distance by, in progress of improvement Hence: Inferior to in dignity, rank, knowledge, or excellence, or in any achievement.
5. Left after the departure of, whether this be by removing to a distance or by death.
6. Not yet brought forward, produced, or exhibited to view; out of sight; remaining.
7. On the side opposite the front or nearest part; on the back side of; at the back of; on the other side of; as, behind a door; behind a hill.
8. The backside; the rump.
9. Toward the back part or rear; backward; as, to look behind.
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rear (part of speech: noun)