Green’s Dictionary of Slang

earlier use in phr cry cave; 20C associated with (fictional) UK schoolboys: look out!

1584		Greene Carde of Fancie 7: Nowe thou wilte crye Caue when thy coyne is consumed, and beware when thy wealth is wracked.
1612		J. Davies Muses sacrifice 159: And that’ because the Dead, in silence, cry / Cave to those, that, liuing, are to dye.
1647		J. Trapp A commentary or exposition upon all the Epistles 282: Warn them that are unruly] Cry Cave miser, stop them in their cursed carier, tell them that hell gapes for them.
1658		T. Hall A practical and polemical commentary 124: [T]he white Devill is the worst, and most dangerous; and therefore when they cry Ave, do thou cry Cave.
1833		Satirist (London) 7 July 7/1: Cave! cave! Sir Tommy.
1855		Luton Times 24 Apr. 8/5: Cave, adsam; you understand me, / Drop them, abandon blague and cant, / And tell me plainly what you want.
1858		F.W. Farrar Eric I 25: ‘Cavè, cavè!’ whispered half a dozen voices.
1864, 1867, 1870		Hotten Sl. Dict.
1883		T.B. Reed Willoughby Captains (1887) 280: At length, however, while the result was still undecided, a cry of ‘Cave!’ was raised.
1899		Kipling ‘An Unsavoury Interlude’ in Complete Stalky & Co. (1987) 93: ‘Cave!’ in an undertone. Beetle had spied King sailing down the corridor.
1900		Boy’s Own Paper 20 Oct. 37: I rushed in crying, ‘Cave! Look out! – the new master!’.
1910		Magnet 27 Aug. 3: ‘Cave!’ said Mark Linley.
1920		Marvel 9 Oct. 14: Cave! [...] The Head’s coming along the corridor.
1930		M. Allingham Mystery Mile (1982) 326: ‘Cave,’ he whispered.
1945		(con. 1937) R. Westerby Mad in Pursuit 189: ‘Bags I,’ they said [...] ‘Cave!’ ‘Pax!’.
1959		I. & P. Opie Lore and Lang. of Schoolchildren (1977) 214: Cave! Someone’s coming.
2000		Indep. on Sun. Culture 23 July 1: In 1969, one warned fellow pupils of the approach of a master by saying ‘cave’, the Latin word for ‘beware’; by the time I left, the tradition was breaking down.