dover’s powder, n. — Green’s Dictionary of Slang

dover’s powder n.

also dover’s deck

[proper name Thomas Dover (1660–1742), an English physician whose patented preparation of opium and ipecacuanha (Pulvis doveri) was used as a pain-killing medicine]

(drugs) opium.

[1845		Liverpool Mercury 7 Nov. 10/6: Merchant Seamen’s Act:— Medicines: quantities for 10 men. Castor oil, I lb [...] Dover’s powder, 2 oz; mustard, 1 lb].
[1871		Liverpool Mercury 9 May 8/5: The husband sent up two powders [...] one consisting of five grains of Dover’s powder [...] The powder administered to the child contained opium in more than suffficient quantity to cause death].
2001		ONDCP Street Terms 8: Dover’s deck — Opium; Dover’s powder — Opium.