Green’s Dictionary of Slang

1. a guinea.

1688		T. Shadwell Squire of Alsatia I i: Prithee, noble squire, equip me with a couple of megs, or two couple of smelts.
c.1698		B.E. Dict. Canting Crew n.p.: Meggs c. Guineas. We fork’d the rum Cull’s Meggs to the tune of Fifty, c. We Pickt the Gentleman’s Pocket of full Fourty Guineas.
1709		N. Ward Compleat and Humorous Account of Remarkable Clubs (1756) 228: Then on with your Night-Caps and tie up your Legs, / A Begging let’s go for the Smelts and the Megs.
1719		A. Smith Lives of Most Notorious Highway-men, etc. (1926) II [as cit. c.1698].
1725		New Canting Dict. [as cit. c.1698].
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. c.1698].
c.1750–1882		B.M. Carew Life and Adventures.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Meggs, guineas, (cant).
1859		Hotten Dict. of Modern Sl. etc. 61: meggs were formerly guineas.
1860		Hotten Dict. of Modern Sl. etc. [as cit. 1859].

2. (US) a silver coin, from ten cents (a dime) to a dollar.

1910		Spokane Press (WA) 22 Sept. 7/3: The best draw made [...] was thirty megs (dollars).
1917		R. Lardner ‘Three Kings and a Pair’ in Gullible’s Travels 62: Some doll she was, too, in a fifty-meg evenin’ dress marked down to thirty-seven.
1926		Maines & Grant Wise-crack Dict. 11/1: Meg – Any denomination of silver money between ten cents and one dollar, signified by fifteen megs, twenty megs, etc.
1987		W.T. Vollmann You Bright and Risen Angels (1988) 314: Here’s how we clean out their cush, their C-notes and megs, their deemers and crisp green bumblebees.

3. (US) a cent.

1915		Morn. Tulsa Dly World (OK) 13 June 19/3: Meg — A penny.
1920		A. Baer [no title] 10 Aug. [synd. col.] Hot dogs are up to ten megs apiece.
1920		A. Baer Says ’Bugs’ Baer 15 Nov. [synd. col.] Admission will be from fifty megs to a dollar.

4. see mag n.³