Green’s Dictionary of Slang

(UK Und.) milk; thus poplars of yarrum, milk porridge.

c.1566		Harman Caveat for Common Cursetours in Viles & Furnivall (1907) 83: yaram mylke.
1592		Groundworke of Conny-catching A3: She hath a Cackling Chete, a gruntinge chete, ruffe peck, cassan, and popelars of yarum.
1608		Dekker Lanthorne and Candle-Light Ch. 1: If we mawnd Pannam, lap, or Ruff-peck / Or poplars of yarum.
1610		Rowlands Martin Mark-all 41: Yarrim pottage or milke.
1641		R. Brome Jovial Crew II i: Here’s Pannam and Lap, and good Poplars of Yarrum, / To fill up the Crib, and to comfort the Quarron.
1665		Head Eng. Rogue I 53: Yarum, Milk.
1674		‘The Beggars Curse’ Head Canting Academy (1674) 14: If we maund Pannam, lap, or ruff peck / Or poplars of Yarum.
1688		R. Holme Academy of Armory Ch. iii item 68c: Canting Terms used by Beggars, Vagabonds, Cheaters, Cripples and Bedlams. [...] Yarrume, Milk.
c.1698		B.E. Dict. Canting Crew n.p.: Yarum, c. Milk.
1714		A. Smith Lives of Most Noted Highway-men, etc. I 209: He taught his Pupil a deal of canting Words, telling him [...] Yarum, was Milk.
1725		New Canting Dict. n.p.: yarum Milk, or Food made of Milk.
1728		Defoe Street Robberies Considered 35: Yarm, Milk.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Yarum, milk, (cant).
1809		G. Andrewes Dict. Sl. and Cant n.p.: Yarum food made of milk.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1835		G. Kent Modern Flash Dict.
1848		Flash Dict. in Sinks of London Laid Open.
c.1850		Duncombe New and Improved Flash Dict. n.p.: Yarum food made of flour and milk.
1859		Matsell Vocabulum 97: yavum [sic] Bread and milk.
1895		Crowe Aus. Sl. Dict. [as 1859].