late 14c., "to change (something), make different in some way," from Old French alterer "to change, alter," from Medieval Latin alterare "to change," from Latin alter "the other (of the two)," from PIE root *al- (1) "beyond" + comparative suffix -ter (as in other). Intransitive sense "to become otherwise" first recorded 1580s. Related: Altered; altering.

"to contend with words," 1520s, a back-formation from altercation, or else from Latin altercatus, past participle of altercari "to dispute (with another)," from alter "the other" (see alter).

mid-15c., from Old French alternacion "alternation," from Latin alternationem (nominative alternatio) "an interchanging," noun of action from past-participle stem of alternare "to do first one thing then the other; exchange parts," from alternus "one after the other, alternate, in turns, reciprocal," from alter "the other" (see alter).

c. 1500, "act of adulterating; state of being debased by mixture with something else," generally of inferior quality, from Latin adulterationem (nominative adulteratio) "an adulteration, sophistication," noun of action from past-participle stem of adulterare "corrupt, falsify; debauch; commit adultery," from ad "to" (see ad-) + alterare "to alter" (see alter), though Watkins explains it as ad alterum "(approaching) another (unlawfully)." Meaning "a result of adulterating" is from 1650s.

late 14c., altercacioun, "angry contention with words," from Old French altercacion "altercation" (12c.) and directly from Latin altercationem (nominative altercatio) "a dispute, debate, discussion," noun of action from past-participle stem of altercari "to dispute (with another)," from alter "the other" (see alter). The notion perhaps is of "speaking alternately."

Altercation is the spoken part of a quarrel, the parties speaking alternately. An altercation is thus a quarrelsome dispute between two persons or two sides. [Century Dictionary]