do a bit

do a bit

1. To do only a small amount of something. I was only able to do a bit of cleaning before your mother called—that's why the dirty dishes are still on the table. A: "Did you write your essay?" B: "I did a bit, but I decided to take a break.
2. To tell a joke or perform a short comic routine, especially when done in a satirically serious or sincere manner. The comic has such a dry sense of humor that it can sometimes be hard to tell when he's doing a bit or actually being serious.
See also: bit
Farlex Dictionary of Idioms.

do (one's) bit

To make an individual contribution toward an overall effort.
See also: bit
American Heritage® Dictionary of the English Language, Fifth Edition.
See also:
  • draw the line at
  • draw the line at (something)
  • all y'all's
  • a world of
  • a world of (something)
  • bone of contention
  • contention
  • a bone of contention
  • pile up
  • beat (one's) gums
References in classic literature
And that's reasonable; for if Old Harry's a mind to do a bit o' kindness for a holiday, like, who's got anything against it?
Silas Marner
"My education has always been a big deal to me and my two sisters were naturally clever and passed with flying colours - but I needed to do a bit more revision.
We filmed the moment an 18-year-old opened her A Levels - and it was brilliant; Emotional video shows exactly what results day can mean for nervous students