Green’s Dictionary of Slang

1. (orig. US) to understand.

1859		Hotten Dict. of Modern Sl. etc. 12: BROWN-TO, to understand.
1866		Wild Boys of London I 234/1: We’ll have a peeler in the aery ready, don’t yer brown?
1872		Schele De Vere Americanisms 587: Brown, to, is occasionally met with in the sense of to understand, and as such quoted as ‘American Slang’ in the Slang Dictionary (p. 86). Its use is very rare, but the meaning is evidently connected with the familiar slang phrase, to do a thing brown.
1879		London Life 8/1: Do you Brown to it?
1880		W. Hooe Sharping London 34: Brown, to be aware of.
1888		Sporting Times 27 Oct. 1/3: Do you tumble, Mrs Simmonds, do you brown?
1890		Dead Bird (Sydney) 22 Feb. 3/2: And with dread he was racked when he browned to the fact / That her friend was his uncle — Good night!
1891		Sporting Times 18 Apr. 3/5: Jenny Hill [...] is at Pastor’s, in New York. New York audiences have hardly browned to her slang as yet, where she has had some glossaries printed and given away at the doors.
1897		Marshall Pomes 38: You will easily brown that the case was dismissed by the beak, with a frown [F&H].
1902		Sheffield Wkly Teleg. 8 feb. 20/3: ‘I comes ’ome, and my missus she jaws me out for bein’ boozed, so I gives her one for herself. D’ye brown?’ Magistrate: ‘I scarcely understand what is meant by “brown”.’ Clerk: ‘It means “Do you understand?”’.
1909		J. Ware Passing Eng. of the Victorian Era 50/2: Brown to (Com. Classes). To understand. Origin very obscure – probably from a keen man of this name. ‘He didn’t brown to what she was saying – not a little bit.’.

2. to get the better of, to surpass; in cit. 1942, to kill.

1837–8		‘Slashing Costermonger’ in Cuckold’s Nest 10: I’ve got a leery moke asides, / All others he does brown, sirs.
1899		Kipling ‘Slaves of the Lamp — Part II’ in Complete Stalky & Co. (1987) 289: Stalky was brownin’ ’em at a great rate.
1934		(con. 1920s) J.T. Farrell Young Manhood in Studs Lonigan (1936) 185: ‘We’ll brown the Kaiser,’ shouted Kenny.
1942		R.L. Bellem ‘Broken Melody’ in Dan Turner – Hollywood Detective Dec. 🌐 Like a sap, I took my lamps off you for a minute. And you browned her.