1859. Matsell, Vocabulum, or Rogue’s Lexicon, s.v.
Verb (public schools’).—1. To do menial work for a schoolfellow in a
higher form. Cf., Fag, subs., sense 1.
1884. Temple Bar, August, p. 514. He must have completely marred
his chance of happiness at the school when he refused to fag and
took countless thrashings, snivelling.