/ Dictionary / Index S sis: Meaning and Definition of Find definitions for: sis Pronunciation: (sis), [key] — n. Informal. sister. -sis Pronunciation: [key] a suffix appearing in loanwords from Greek, where it was used to form from verbs abstract nouns of action, process, state, condition, etc.: thesis; aphesis. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: sis (Thesaurus) sirvente sisal Related Content Daily Word Quiz: blanch Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language