/ Dictionary / Index A active hydrogen: Meaning and Definition of Find definitions for: ac'tive hy'drogen Pronunciation: [key] — Chem. Chem. See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. active duty active immunity Related Content Daily Word Quiz: blithesome Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language