/ Dictionary / Index P propionaldehyde: Meaning and Definition of Find definitions for: pro•pi•on•al•de•hyde Pronunciation: (prō"pē-on-al'du-hīd"), [key] — n. Chem. a colorless, water-soluble liquid, CHO, having a pungent odor: used chiefly in the manufacture of plastics. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: propionaldehyde (Thesaurus) propinquity propionate Related Content Daily Word Quiz: opulent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language