/ Dictionary / Index E equivalence principle: Meaning and Definition of Find definitions for: equiv'alence prin"ciple Pronunciation: [key] — Physics. Physics. (in relativity) the principle that, in any small region of space-time, the effects of a gravitational field are indistinguishable from those of an appropriate acceleration of the frame of reference. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. equivalence class equivalence relation Related Content Daily Word Quiz: paradox Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language