Green’s Dictionary of Slang

1. to complain.

1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: To grunt; to groan, or complain of sickness.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1915		H.E. Rollins ‘A West Texas Word List’ in DN IV:iii 226: grunt, v. To complain.

2. (US) to do menial work.

1938		W.W. Haines High Tension 104: A guy that’s just good couldn’t grunt for him at the piano.
1945		F.H. Hubbard Railroad Avenue 345: Grunting is working as a lineman’s helper.

3. (US) to defecate.

1967–8

Baker et al. CUSS.

4. (UK juv.) to break wind.

2001

OnLine Dict. of Playground Sl. 🌐 grunt v. to break wind.