im·ma·ture (?m??-tyo?or?, -cho?or?, -to?or?)adj.1. Not fully grown or developed: an immature plant.2. Marked by or suggesting a lack of normal maturity: silly, immature behavior. See Synonyms at young.n. An immature animal; a juvenile.[Latin imm?t?rus : in-, not; see in-1 + m?t?rus, mature; see m?- in Indo-European roots.]im?ma·ture?ly adv.im?ma·tur?i·ty, im?ma·ture?ness n.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.immature (??m??tj??; -?t???) adj1. not fully grown or developed2. deficient in maturity; lacking wisdom, insight, emotional stability, etc3. (Physical Geography) geography a less common term for youthful4 ?imma?turity, ?imma?tureness n ?imma?turely advCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014im?ma?ture (??m ??t???r, -?t??r, -?ty??r, -?t??r) adj. 1. not mature or ripe. 2. emotionally undeveloped; juvenile; childish. 3. youthful (def. 4). 4. Archaic. premature. [1540?50;