/ Dictionary / Index P pentamethylene: Meaning and Definition of Find definitions for: pen•ta•meth•yl•ene Pronunciation: (pen"tu-meth'u-lēn"), [key] — n. Chem. cyclopentane. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. pentameter pentamethylenediamine Related Content Daily Word Quiz: procrastinate Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language