a. [ L. infantilis: cf. F. infantile. See Infant. ] Of or pertaining to infancy, or to an infant; similar to, or characteristic of, an infant; childish;
. (Med.) An acute viral disease, affecting almost exclusively infants and young adults, characterized by inflammation of the anterior horns of the gray substance of the spinal cord. It is attended with febrile symptoms, motor paralysis, and muscular atrophy, often producing permanent deformities. Called also