mutabilis

Etymology
From.

Adjective

 * 1) mutable, changeable, inconstant
 * 2) * Albertus Oelingerus, Underricht der Hoch-Teutschen Spraach: Grammatica seu institutio verae Germanicae linguae, in qua Etymologia, Syntaxis & reliquae partes omnes suo ordine breviter tractantur. 1574, p. 2 (books.google):
 * Et dividuntur quoque vocales, in mutabiles & immutabilies, more Graecorum. Mutabiles sunt tres. a mutatur in ä vel ä vel e, o mutatur in ö vel ö, u mutatur in ü.
 * And the vowels are also divided, into changeable & unchangeable vowels, in the custom of the Greeks. Changeables are three. a is changed into ä (or ä) or e, o is changed into ö (or ö), u is changed into ü.