do a bit—
1. perform a small part in a play or movie:
- I got to do a bit with Mick Jagger where he comes into a dressing room and looks in the mirror….
2. practice smth. in a small way:
- In my spare time I always want to do something “creative,” so I choose to do a bit of carpentering.
do one’s bit—
1. fulfill one’s responsibilities or obligations:
- During the epidemic he did his bit with the other physicians, attending cases night and day.
2. make one’s contribution to the war effort (serving in the armed forces, etc.):
- Yes we did our bit, as you folks say. I’ll tell the world we got the enemy on the run.