1894 in the psychological sense; see infantile + -ism. Earlier in a physiological sense, "retarded and imperfect physical development," perhaps from French infantilisme (1871).
Entries linking to infantilism
infantile adj.
mid-15c., "pertaining to infants," from Late Latin infantilis "pertaining to an infant," from infans "young child" (see infant). Sense of "infant-like" is from 1772.
-ism
word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.