ADJ. faint, soft | low | high-pitched | constant, continuous, steady I could hear the constant hum of distant traffic. | background
VERB + HUM hear
PREP. ~ of the background hum of the air-conditioning
ADV. quietly, softly | happily | tunelessly | along humming along with the music
VERB + HUM begin to He began to hum, somewhat tunelessly.
PHRASES hum to yourself She was humming softly to herself.