The Collaborative International Dictionary of English v.0.48:
Fag \Fag\, v. i. [imp. & p. p. Fagged (f[a^]gd); p. pr. & vb.
n. Fagging (f[a^]g"g[i^]ng).] [Cf. LG. fakk wearied, weary,
vaak slumber, drowsiness, OFries. fai, equiv. to f[=a]ch
devoted to death, OS. f[=e]gi, OHG. feigi, G. feig, feige,
cowardly, Icel. feigr fated to die, AS. f[=ae]ge, Scot. faik,
to fail, stop, lower the price; or perh. the same word as E.
flag to droop.]
1. To become weary; to tire.
Creighton withheld his force till the Italian began
to fag. --G.
2. To labor to wearness; to work hard; to drudge.
Read, fag, and subdue this chapter. --Coleridge.
3. To act as a fag, or perform menial services or drudgery,
for another, as in some English schools.
To fag out, to become untwisted or frayed, as the end of a
rope, or the edge of canvas.