The definition of alter means to make something different without completely changing it.(verb)
An example of alter is to cut a few inches off the bottom of a dress to make it shorter.
See alter in Webster's New World College Dictionary
Origin: ME alteren < ML alterare < L alter, other < IE *al- (see else) + -tero-, compar. suffix
See alter in American Heritage Dictionary 4
verb al·tered, al·ter·ing, al·ters verb, transitive
Origin: Middle English alteren
Origin: , from Old French alterer
Origin: , from Medieval Latin alterāre
Origin: , from Latin alter, other; see al-1 in Indo-European roots.
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