Green’s Dictionary of Slang

fag n.2

[SE fag, to tire, to perform a wearisome task; ? ult. flag v., to droop, to tire]

1. a bore, a chore, an unpleasant, tedious task .

[UK]Mme D’Arblay Diary and Letters (1904) I 340: This was my fag till after tea.
[UK]H. Nelson Dispatches & Letters (1845) III 43: As no fleet has more fag than this, nothing but the best food and greatest attention can keep them healthy .
[UK]J.M.F. Wright Alma Mater I 248: This afternoon’s fag is a pretty considerable one, lasting from three till dark.
[UK]Navy at Home I 86: Such is the state of worry, distraction, and never ceasing fag of a first lieutenant of a man of war.
[Ire]S. Lover Handy Andy 178: Nectar and ambrosia for tea and bread-and-butter, could not tempt them from the christian enjoyment of a feather-bed after the fag of such a day.
[US]B.H. Hall College Words (rev. edn) 188: fag. Time spent in, or period of, studying.
[Aus]Dead Bird (Sydney) 26 Apr. 4/1: And no matter the fag, I don’t shun it.
[UK]Boy’s Own Paper 12 Aug. 730: And bicycling began to be a fag.
[Aus]Bulletin (Sydney) 26 Jul. 14/4: Miss Jenkins found the theatrical life irksome in the extreme, the moving of goods and chattels a frightful fag.
[Aus]Sun. Times (Perth) 29 Dec. 1/1: Members of the W.A. Government Party are enjoying a ‘well-earned rest.’ [...] The brain-fag incidental to their recent herculean labors is apparent.
[UK]Wodehouse ‘Pillingshot’s Paper’ in Captain Feb. [Internet] Do you realise what it means to found a paper—the expense, the months of brain-fag, the worry?
[Aus]C.E.W. Bean Anzac Book 109/1: It must be a fag getting the oil you liked so much. I suppose you have to walk some distance from the firing-line to the nearest shops.
[UK]Marvel 3 Mar. 7: I don’t want the additional fag of shutting it myself.
[UK](con. 1900s) S. Leslie Oppidan 56: A year passed before Peter glanced at one of those well-established preventives of brain fag.
[UK]‘George Orwell’ Keep The Aspidistra Flying (1962) 208: It’s too much fag to shave every day.
[UK]A. Christie Body in the Library (1959) 63: Don’t usually bother [...] Such a fag putting a car away in a garage.
[UK]A. Buckeridge Jennings Goes To School 243: It’s a bit of a hairy fag, of course.
[UK](con. c.1920) D. Holman-Hunt My Grandmothers and I (1987) 116: What a fag! I wish we hadn’t got to do it.
[UK]P. Theroux Family Arsenal 123: Sometimes I don’t think I can bear it a minute more. It’s such a fag.
[UK]Guardian G2 5 July 6: Exercise is so dull and such a fag.

2. a hard worker.

[Ire]J. O’Keeffe London Hermit (1794) 17: You were always a dead fag [i.e. at Cambridge University], and I was a blood.
[US]B.H. Hall College Words (rev. edn) 188: fag. A diligent student.
[US]Baker et al. CUSS 114: Fag A person who studies a great deal.

In compounds

brain fag (n.)

mental exhaustion.

[US]W. Irwin ‘Prologue’ in Love Sonnets of a Hoodlum n.p.: Brain-fag wrecks who want to keep it dark Just why their crop of thinks is running small.
[Aus]E. Dyson Missing Link [Internet] Ch. xiii: He passed quite easily for a dramatic artist taking rest and change to dissipate brain fag, the result of too studious application to his art.
[UK]Whizzbang Comics 73: I’m on war work. Down here with brain fag.

In phrases