/in"feuhn tl iz'euhm, -tuy liz'-, in fan"tl iz'euhm/ , n.
1. the persistence in an adult of markedly childish anatomical, physiological, or psychological characteristics.
2. an infantile act, trait, etc., esp. in an adult.
3. a speech disorder characterized by speech and voice patterns that are typical of very young children.
[ 1890-95; INFANTILE + -ISM ]