Green’s Dictionary of Slang

non-existent, absent.

1846		Bell’s Life in Sydney 28 Mar. 2/6: In consequence of G. U. A’s. deficiency of ‘tin,’ he was non est; but he sent a letter to the magistrates.
1849		Paul Pry 8 Jan. 7/2: What has become of that egregious fop, with moustachios and a red smoking cap [...] Paul thinks that the trade is on the decline, as he is non est.
1865		Leaves from Diary of Celebrated Burglar 96/2: Joe and I walked from one table to another, speaking to such as either of us knew; but the individual we we were in quest off [sic] was non est.
1872		G.P. Burnham Memoirs of the US Secret Service 55: McCartney’s wife had also been arrested. But Pete was non est. at the time the Louisville police entered.
1913		Sport (Adelaide) 26 July 10/4: Are railway men non est, May?
1959		R. Fuller That Distant Afternoon 34: The weights you put on it at the end of the arm thing were non est. They all had to search the big box-room.