reverse

Reverse denotes the action, position, or state of turning back or moving in the opposite direction. As an adjective, it describes something facing backward or opposite to the usual direction, such as the reverse gear on a vehicle or the reverse side of a coin. As a noun, it can refer to the opposite side of an object or to a reversal in a policy, plan, or sequence. As a verb, to reverse means to turn around, to move backward, or to undo a previous action or condition.

In everyday use, reversing is common in travel and mechanics, where a vehicle may be put into reverse to move backward, or a route or plan may be reversed to adopt the opposite course. In law and governance, a court may reverse a decision on appeal, restoring or altering the legal outcome. The phrase in reverse is used to describe movement or action in the opposite direction.

In mathematics and computer science, reverse relates to the inverse concept: reversing an operation undoes its effect, such as inverse functions or opposite operations. Reversing a sequence, string, or array yields elements in the opposite order. In engineering and science, reverse terms appear in processes like reverse osmosis or reverse engineering, where a system is analyzed to understand and replicate its design.

Etymology: reverse derives from Latin reversus, the past participle of revertere, meaning to turn back, via Old French and Middle English. The word has a wide range of compounds and idiomatic uses, including “reverse,” “in reverse,” and “reverse course.”