The Collaborative International Dictionary of English v.0.48:
low-key \low-key\ low-keyed \low-keyed\adj. restrained in style or quality; not flashy or intense; understated; as, a little masterpiece of low-keyed eloquence. Syn: subdued. [WordNet 1.5]WordNet (r) 3.0 (2006):
low-key adj 1: restrained in style or quality; "a little masterpiece of low-keyed eloquence" [syn: low-key, low-keyed, subdued]