1. To make a buzzing sound; SYN. bombinate, bombilate.
2. To fly low.
3. To call with a buzzer.

ETYM Old Eng. croinen, cf. Dutch kreunen to moan.
To sing softly.
1 chiefly Scottish; bellow, boom.
2. To sing or speak in a gentle murmuring manner; especially; to sing in a soft intimate manner adapted to amplifying systems.
3. To sing (as a popular song or a lullaby) in a crooning manner.

1. To sing with closed lips.
2. To make a low continuous sound.
3. To sound with a monotonous hum; SYN. thrum.
4. To be noisy with activity; SYN. buzz, seethe.

A humming noise; SYN. humming.