to-be (to?o-b??)adj. That is to be; future. Often used postpositively and in combination: a graduate-to-be.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.to-be? adj. future; soon to be as specified: bride-to-be. [1590?1600] Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.