English▸ noun [in singular] informal, mainly British a tiring or unwelcome task:
it's too much of a fag to drive all the way there and back again.
▪ British a junior pupil at a private school who works and runs errands for a senior pupil.
▸ verb
(fags, fagging, fagged)
[no object] informal work hard, especially at a tedious job or task: he didn't have to fag away in a lab to get the right answer.
▪ (of a pupil at a private school) work and run errands for a senior pupil.
– ORIGIN mid 16th century (as a verb in the sense ‘grow weary’): of unknown origin. Compare with flag4.