/ Dictionary / Index S sinoatrial node: Meaning and Definition of Find definitions for: si'no•a'tri•al node' Pronunciation: (sī'nō-ā'trē-ul, sī"-), [key] — Anat. Anat. a small mass of tissue in the right atrium functioning as pacemaker of the heart by giving rise to the electric impulses that initiate heart contractions. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. sino- Sino-Japanese War 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