/ Dictionary / Index Y ylem: Meaning and Definition of Find definitions for: y•lem Pronunciation: (ī'lum), [key] — n. the initial substance of the universe from which all matter is said to be derived. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: ylem (Thesaurus) ylang-ylang YMCA Related Content Daily Word Quiz: immense Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language