behind

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adverb In, to, or toward the rear.
• adverb In a place or condition that has been passed or left.
• adverb In arrears; late.
• adverb Below the standard level; in or into an inferior position.
• adverb Slow.
• adverb Archaic Yet to come or in reserve.
• preposition At the back of or in the rear of.
• preposition On the farther side or other side of; beyond.
• preposition In a place or time that has been passed or left by.
• preposition Later than.
• preposition Used to indicate deficiency in performance.
• preposition Hidden or concealed by.
• preposition In the background of; underlying.
• preposition In a position or attitude of support.
• preposition In pursuit of.
• noun Informal The buttocks.

from The Century Dictionary.

• At the back of some person or thing; in the rear: opposed to before.
• Toward the back part; backward: as, to look behind.
• Out of sight; not produced or exhibited to view; in abeyance or reserve.
• Remaining after some occurrence, action, or operation: as, he departed and left us behind.
• Past in the progress of time.
• In arrear; behindhand: as, he is behind in his rent.
• At the back or in the rear of, as regards either the actual or the assumed front: the opposite of before: as, the valet stood behind his master; crouching behind a tree.
• Figuratively, in a position or at a point not so far advanced as; in the rear of, as regards progress, knowledge, development, etc.; not on an equality with: as, behind the age; he is behind the others in mathematics.
• In existence or remaining after the removal or disappearance of: as, he left a large family behind him.
• Synonyms Behind, After. Behind relates primarily to position; after, to time. When after notes position, it is less close or exact than behind, and it means position in motion. To say that men stood one after another in a line was once correct (see Chaucer, knight's Tale, 1. 901, “kneeled … each after other”), but is not so now. They may come one after another, that is, somewhat irregularly and apart; they came one behind another, that is, close together, one covering another. The distinction is similar to that between beneath and below.

from the GNU version of the Collaborative International Dictionary of English.

• preposition On the side opposite the front or nearest part; on the back side of; at the back of; on the other side of.
• preposition Left after the departure of, whether this be by removing to a distance or by death.
• preposition Left a distance by, in progress of improvement Hence: Inferior to in dignity, rank, knowledge, or excellence, or in any achievement.
• noun Low The backside; the rump.
• adverb At the back part; in the rear.
• adverb Toward the back part or rear; backward.
• adverb Not yet brought forward, produced, or exhibited to view; out of sight; remaining.
• adverb Backward in time or order of succession; past.
• adverb After the departure of another.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• preposition at the back of
• preposition to the back of
• preposition after, time- or motion-wise
• preposition responsible for
• preposition in support of
• adverb At the back part; in the rear.
• adverb Toward the back part or rear; backward; as, to look behind.
• adverb Not yet brought forward, produced, or exhibited to view; out of sight; remaining.
• adverb Backward in time or order of succession; past.
• adverb After the departure of another; as, to stay behind.
• adverb Behind the scenes in a theatre; backstage.
• noun the rear, back-end
• noun bottom, downside