Green’s Dictionary of Slang

a regular private soldier.

1903		Barking, East Ham & Ilford Advertiser 11 July 1/2: George Bishop, private of the Royal Fusliers, was summoned for assaulting Harry Vivian. [...] Complainant said he remarked ‘Hullo, squaddy,’ to the defendant, where therupon struck him in the eyes.
1915		Middlesex Chron. 19 June 3/3: Palmer [...] joined the rest of the waiting ‘squaddies’.
1921		N&Q 12 Ser. IX 344: Squatti. A private.
1945		Uxbridge & W. Drayton Gaz. 12 Jan. 5/1: ‘Four lonely squaddies in Burma’ send greetings to the people of Uxbridge.
1958		(con. 1940s) B. Behan Borstal Boy 169: Geezer of nineteen, a squaddy, ’e was.
1973		B.S. Johnson All Bull 230: The archetypal British Squaddy with his shapeless khaki battledress, furtively puffing at a fag end in the corner of a railway-train corridor.
1977		(con. 1940s) O. Manning Danger Tree 11: A squaddie came to carry his kit.
1983		S. Gee Never in My Lifetime in Best Radio Plays (1984) 53: I can see this squaddie’s boots go squelching by.
1983		T. Paulin ‘Desertmartin’ in Liberty Tree 16: A Jock squaddy glances down the street.
1998		Guardian G2 19 Nov. 6: A group of drunken squaddies.
2004		C. Brookmyre Be My Enemy 166: The purpose of the construction was not to get the squaddies over the drink.
2010		K. Richards Life 371: We could be cool together under stress, like two squaddies.
2011		J.J. Connolly Viva La Madness 70: He looked like a squaddie off to batter insurgents down in Malaya.
2018		I. Welsh Dead Man’s Trousers 31: The violent, bullying squaddie.
2024		J. Meades Empty Wigs (t/s) 591: [T]hey were so obviously cut from the same cloth - itchy, squaddy-issue cloth: [...] happier in the company of horses.