/ Dictionary / Index S synaptic cleft: Meaning and Definition of Find definitions for: synap'tic cleft' Pronunciation: [key] — Physiol. Physiol. the small gap, measured in nanometers, between an axon terminal and any of the cell membranes in the immediate vicinity. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. synapte synarthrodia Related Content Daily Word Quiz: fidelity Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language