Yes, hum is a Scrabble word!

Verb

1. Sing with closed lips

2. Be noisy with activity

3. Sound with a monotonous hum

4. Make a low continuous sound

Noun

1. The state of being or appearing to be actively engaged in an activity

2. An Islamic fundamentalist group in Pakistan that fought the Soviet Union in Afghanistan in the 1980s; now operates as a terrorist organization primarily in Kashmir and seeks Kashmir's accession by Pakistan

3. A humming noise