alternant
[ɔːlˈtəːnənt, ɒl-]noun
an alternative form of a word or other linguistic unit; a variant
（词或其他语言单位的）交替形式
adjectivechanging from one to the other; alternating
交互变化；交替的
语源mid 17th cent.: from Latin alternant- 'doing things by turns', from the verb alternare (see alternate)