Breadcrumb Home > Dictionary > Index S sei whale: Meaning and Definition of Find definitions for: sei' whale" Pronunciation: (sā), [key] a rorqual, Balaenoptera borealis, inhabiting all seas: now greatly reduced in number. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. SEIU seize ✖ Related Content Daily Word Quiz: umbrage Analogy of the Day: Today’s Analogy Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language