Definition of "quarter-tone" []

• In musical acoustics, an interval equivalent to one half of a semitone or half-step. The term is loosely applied to a variety of small intervals, especially to enharmonic ones. (noun)

The Century Dictionary (Public Domain)

• "The one borrowed tune on his new album is Thelonious Monk's "Blue Monk," radically recast in a quarter-tone version."
• "I simply applied the same principle to my genetically enlarged gulls, testing them at each quarter-tone past human range before I found exactly the right note."
• "In a series of experiments on Mr. Kennedy's machine, they've thrown several man-sized logs and two quarter-tone dead pigs into the air; one of the pigs parachuted gently back to earth, the other landed rather more forcefully."