/ Dictionary / Index G group theory: Meaning and Definition of Find definitions for: group' the"ory Pronunciation: [key] the branch of mathematics that deals with the structure of mathematical groups and mappings between them. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. group representation group therapy Related Content Daily Word Quiz: endear Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language