/ Dictionary / Index U underground trolley: Meaning and Definition of Find definitions for: un'derground trol'ley. Pronunciation: [key] See under(def. 4). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. underground railroad undergrown Related Content Daily Word Quiz: neologism Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language