Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Sound (Adjective)

Sound as an acorn.
—Anonymous

Sound as a trout.
—Anonymous

Sound as a watch.
—Anonymous

Heart as sound as an oak.
—Beaumont and Fletcher

Sound as old wine.
—Beaumont and Fletcher

Sound as a rock.
—Edward Bulwer-Lytton

Sound-hearted to the core, like some perfect fruit ripened in a sunny nook of an English garden.
—Henry A. Clapp

Sound as a biscuit.
—William Congreve

Sound as a nut.
—Ralph Waldo Emerson

Sound as a roach.
—John Gay

Sound as a fish.
—Martin Luther

Sound as iron.
—Charles Reade

Sound as an honest man’s conscience when he’s dying.
—William Rowley

He hath a heart as sound as a bell, and his tongue is the clapper.
—William Shakespeare

Sound as a top.
—William Makepeace Thackeray