/ Dictionary / Index A acid number: Meaning and Definition of Find definitions for: ac'id num"ber Pronunciation: [key] — Chem. Chem. a number expressing the acidity of a substance, equal to the number of milligrams of potassium hydroxide needed to neutralize the free fatty acids present in one gram of the substance. Also called Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. acid metaprotein acidogenic Related Content Daily Word Quiz: cautious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language