Green’s Dictionary of Slang

(orig. US) splendid, fine, excellent, first-rate.

1823		J. Neal Errata II 175: Run agin me, run agin a snag [...] jam-up.
1841		Southern Literary Messenger VII 54/2: Reaching him a hand, Received him, introduced him to ‘the jam-up little company’ in his command [DA].
1843		T. Haliburton Sam Slick in England I 24: I got them to look considerable jam again.
1855		T. Haliburton Nature and Human Nature II 261: Connubial bliss, I allot, was real jam up.
c.1858		J.H. Green Reformed Gambler 120: Give us a jam-up prayer; and blow and strike out as loud as ye can.
1862		E.K. Wightman letter 28 Oct. in Longacre From Antietam to Fort Fisher (1985) 70: Salt pork, raw onions and crackers made a ‘jam-up’ supper.
1872		Schele De Vere Americanisms 611: Jam up, from the verb to jam, denotes a high degree of perfection.
1881		‘Bill Nye’ Bill Nye and Boomerang 25: My own and only jam-up and scrumptious show.
1897		W.S. Maugham Liza of Lambeth (1966) 5: This is jam!
1905		‘Central Connecticut Word-List’ in DN III:i 12: jam up, adj. First rate.
1912		N.Y. Tribune 1 Sept. 28/2: That’ll be a jam load for the motor.
1921		N&Q 12 Ser. IX 346: Jam. Good.
1931		K.C. Times 21 Aug. n.p.: This [...] perchance truthful comment [...] has been quoted approvingly by [...] other jam-up papers [DA].
1946		Mezzrow & Wolfe Really the Blues 97: It promised a rare jam-up kick, some once-in-a-life thrill.
1957		‘Weldon Hill’ Onionhead (1958) 192: Man, you must be jam-up right, cause sherbet don’t shake like that’.
1962		(con. WWII) J.O. Killens And Then We Heard The Thunder (1964) 69: She’s a first sergeant in the Engineers and doing a jam-up job.
1968		K. Brasselle Cannibals 389: He’s been jam-up, no question about it. Helluva guy.
2000		(con. 1940s–60s) Décharné Straight from the Fridge Dad.
2008		D. Jenkins Franchise Babe 107: [A] jam-up mother-daughter combo, the kind that would entice a man to buy them automobiles in assorted colors.