al·ter / ˈôltər/ • v. [tr.] change or cause to change in character or composition, typically in a comparatively small but significant way: Eliot was persuaded to alter the passage [intr.] our outward appearance alters as we get older. ∎  make structural changes to (a building): plans to alter the dining hall. ∎  tailor (clothing) for a better fit or to conform to fashion: skirts with the hemlines altered a dozen different times. ∎  castrate or spay (a domestic animal).DERIVATIVES: al·ter·a·ble adj.

alter XIV. — (O)F. altérer — late L. alterāre, f. alter other.
So alteration XIV. — (O)F. or late L.