/ Dictionary / Index L lengthen: Meaning and Definition of Find definitions for: length•en Pronunciation: (lengk'thun, leng'-, len'-), [key] — v.t. to make longer; make greater in length. —v.i. to become greater in length; grow long or longer. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: lengthen (Thesaurus) length between perpendiculars length over all Related Content Daily Word Quiz: arboreal Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language