A soft or effeminate boy or man; a male overly attached to his mother: the stale old mama's-boy-liberated-by-looneylovely(1896+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with mamas boy
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.
[ ; mid-1800s