Green’s Dictionary of Slang

(orig. school/university) an umbrella.

1866		Mansfield School-Life at Winchester College (1870) 202: Brolly – An umbrella.
1873		Sl. Dict. 98: Brolly, an umbrella. Term used at both Oxford and Cambridge Universities.
1885		Edinburgh Eve. News 7 Oct. 3/5: And so the ramshackle old brolly is histed [sic] above ’em once more.
1888		Punch 6 June 273: Pair o’ pattens and brolly are more in your line [F&H].
1898		Binstead & Wells Pink ’Un and Pelican 225: He proceeded [...] to walk three times round the fallen brolly.
1900		‘Doss Chiderdoss’ ‘The Food Influence’ Sporting Times 27 Jan. 1/4: She went for the fair and affectionate Floss / With her stout and redoubtable ‘brolly’.
1905		Sun. Times (Perth) 12 Nov. 1/6: A ‘severely cross-examined’ woman witness bashed a lawyer with a brolly.
1910		Bulletin (Sydney) 18 Aug. 10/1: Then I grab my hat and paper – take my brolly up and run / For the tram that meets the ferry, conscious that I’m stoked till One.
1922		Joyce Ulysses 403: Any brollies or gumboots in the fambly?
1937		J. Curtis You’re in the Racket, Too 120: I’ll chuck in this smother and brolly.
1949		P. Pringle Boy’s Book of Cricket 61: Tucking it under your arm like a brolly is a good idea.
1959		C. MacInnes Absolute Beginners 121: The men looking like dutiful schoolkids with their briefcases and brollies.
1965		D. Martin Hero of Too 262: The Mallee fowl starts to stomp with the owl / Under the brolga’s brolly – by Jingo!
1977		Eve. News (London) 17 Aug. 2: Sometimes they swap their City suits and brollies for overalls.
1982		Beano 13 Nov. 6: Why not use the brolly as a boat?
1997		C. Newland Scholar 270: I thought she was gonna bash her with her brolly.
2000		Indep. Rev. 22 Jan. 20: A nasty downpour [...] Brollies at the ready!
2011		J.J. Connolly Viva La Madness 49: Just cos you wanna sit under a brolly.