/ Dictionary / Index B betweenbrain: Meaning and Definition of Find definitions for: be•tween•brain Pronunciation: (bi-twēn'brān"), [key] — n. the diencephalon. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: betweenbrain (Thesaurus) between between-deck Related Content Daily Word Quiz: mamba Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language