Wiktionary
minor key
n. (context music English) A musical key based upon a minor scale.
WordNet
minor key
n. a key based on the minor scale [syn: minor mode]
Usage examples of "minor key".
Halleck's music still wafted over the room, but it had come out of its minor key, lilting and lively now as though he were trying to lift the mood.
But the tune was still recognizable-in a minor key, wistful rather than sad, and the words were still about this third-rate grifter whose topcoat was always in hock and who sponged off his sister.
Mostly they were in a minor key, but interwoven with majors in a fashion both fascinating and horrible.