1. Of or relating to infants or infancy.
2. Displaying or suggesting a lack of maturity; childish: infantile behavior; an infantile remark.

[Middle English infantil, from Latin īnfantīlis, from īnfāns, īnfant-, infant. See infant.]

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.