Green’s Dictionary of Slang

1. to finish off, to put the finishing touch to.

1833		‘Bob Dusty’ in Lummy Chaunter 72: He’d top off a quartern, and could tell if it was good.
1836		M. Scott Cruise of the Midge II 181: I must top off with some hot brandy and water.
c.1865		‘When I was down to Sweeny’s’ in Fred Shaw’s Champion Comic Melodist 14: And then to have some good frogs’ legs [...] And top off, with two fried eggs.
1891		Century mag. (N.Y.) XLI 47/1: A heavy sleep evolved out of sauerkraut, sausages, and cider, lightly topped off with a mountain of crisp waffles .
1911		E.S. Sorenson Bush Cooks in Life in the Aus. Backblocks 88: On the other hand, if he is rationed out, as at many stations, and allowed none of the extras that help, as bushmen say, to top off a meal, the table naturally suffers, and the best name the men can find for him is ‘poisoner.’.
1917		J.E. Rendinell diary 20 Nov. in One Man’s War (1928) 37: They topped it off with four bottles of cognac.
1924		G.H. Lawson Dict. of Aus. Words And Terms 🌐 TOP OFF — To finish.
1938		N. Lindsay Age Of Consent 78: I think I’ll have a bit of bread and jam to top off with.
1972		N.C. Heard To Reach a Dream 137: ‘She’s always outgoing. Top that off with a slight high and you’ve got what you see tonight’.

2. (Aus.) to knock on the head.

1889

Dead Bird (Sydney) 16 Nov. 4/1: I bleeve if she could ’ave got a ’old of a bottle she’d a topped me off like a toff.

3. (Aus.) to kill, thus top oneself off, to commit suicide.

1910		Sun. Times (Perth) 17 July 2nd sect. 17/7: Four of the five have since suicided [...] a third- topped himself off by hanging.
1919		W.H. Downing Digger Dialects 50: top off (vb.) — Kill.
1924		(con. WWI) A.G. Pretty Gloss. Sl. [...] in the A.I.F. 1921–1924 (rev. t/s) n.p.: top off. To kill.
1933		New Call (Perth, WA) 2 Feb. 17/1: [He was] by no means reluctant to ‘top off’ any of his associates.
1949		Monteleone Criminal Sl. (rev. edn).
1999		D. Looser ‘Boob Jargon’ in NZEJ 13 36: top off v.1. To commit suicide. 2. To kill.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 191/2: top v. 2 (also top off) to kill someone, esp. by hanging. 3 (top off) to commit suicide.

4. (Aus., also top up) to beat up; to prepare to fight.

1901		W.S. Walker In the Blood 101: They fight to make their mark. You would have to be ‘well topped up,’ i.e., your head cracked and yourself left senseless, before they would be satisfied.
1910		L. Esson Woman Tamer in Ballades of Old Bohemia (1980) 62: You’re all talk. Bongo Williams got nine months for topping off a mob o’ Chows with a bottle. He passed out four of them.
1916		C.J. Dennis ‘The Straight Griffin’ in Moods of Ginger Mick 80: Once, when they caught me toppin’ off a John, / The Bench wus stern, an’ torked uv dirty work.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 191/2: top v. 2 (also top off) 4 (top off) to prepare for a fight.

5. (US Und.) to cheat at a dice game.

1933

‘Goat’ Laven Rough Stuff 136: It was there that I first started topping off a dice game.

6. see top v.³ (1)