The Collaborative International Dictionary of English v.0.48:
Alterant \Al"ter*ant\, a. [LL. alterans, p. pr.: cf. F. alt['e]rant.] Altering; gradually changing. --Bacon. [1913 Webster]The Collaborative International Dictionary of English v.0.48:
Alterant \Al"ter*ant\, n. An alterative. [R.] --Chambers. [1913 Webster]