/ Dictionary / Index M methylnaphthalene: Meaning and Definition of Find definitions for: meth•yl•naph•tha•lene Pronunciation: (meth"ul-naf'thu-lēn", -nap'-), [key] — n. Chem. a compound, CH, whose alpha isomer, a colorless liquid, is used in determining cetane numbers. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. methyl methacrylate methyl oleate Related Content Daily Word Quiz: penchant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language