mama's boy definition by American Heritage Dictionary
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A boy or man characterized by unusual closeness to his mother and often by timidity and overly refined manners.
mama's boy - Phrases/Idioms
A sissy, especially a boy or man excessively attached to his mother. For example, The children called Tom a mama's boy because he ran home with every little problem. This sexist expression has survived despite its pejorative tone. [Colloquial; mid-1800s]