inflection (n.)

also inflexion, early 15c., from Middle French inflexion and directly from Latin inflexionem (nominative inflexio) "a bending, inflection, modification," noun of action from past participle stem of inflectere "to bend in, to change" (see inflect). For spelling, see connection. Grammatical sense "variation by declension or conjugation" is from 1660s; pronunciation sense "modulation of the voice" is from c. 1600.
"Derivation" can be defined as the process by which lexical items belonging to different word-classes are drawn from given bases. Derivation must be distinguished from inflexion, by which different paradigmatic forms are created from given stems. Inflexion describes plural formations, forms of comparison, etc. Inflexion processes do not change the word-class to which the lexical item under consideration belongs. [Alfred Bammesberger, "English Etymology," Heidelberg, Carl Winter, 1984]