the act or process of alternating or the state of being alternated.

alternate succession; repeated rotation

the alternation of the seasons.

Electricity . a single fluctuation in the absolute value of an alternating current or voltage from zero to a maximum and back to zero, being equal to one half cycle.

Linguistics . variation in the form of a linguistic unit as it occurs in different environments or under different conditions, as between the -ed and -en forms of the past participle in danced and spoken or between the (t) and (d) pronunciations of the past tense suffix -ed in hopped and rubbed.

noun

variation , rotation , interchange , shift , transposition