Dems|dɛmz| Abbrev. of Defensively Equipped Merchant Ship; a gunner on such a ship. 1943–4Hutchinson's Pict.Hist. War 27 Oct.–11 Apr. 266 Defensively equipped merchant ship gunners (‘Dems’) taking a refresher course... A high-angle 4-in. gun being demonstrated to a ‘Dems’ class.