/ Dictionary / Index A alto clef: Meaning and Definition of Find definitions for: al'to clef" Pronunciation: [key] — Music. Music. a sign locating middle C on the third line of the staff. Also calledSee illus. under Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. alto altocumulus Related Content Daily Word Quiz: boorish Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language