Green’s Dictionary of Slang

splendid, excellent, first-rate; thus adv. splendaciously.

1593		M. Drayton Moses III in Chalmers IV (1810) 488/1: Trumpets celestial sounding as he came [...] Himself invested in a splendorous flame. [Ibid.] 489/1: His brows encircled with splendidious rays.
1605		Jonson Volpone II i: Worshipful merchants, ay, and senators too [...] have detained me to their uses, by their splendidous liberalities.
1630		J. Taylor Works n.p.: To the mirror of time, the most refulgent splendidious reflecting court animal, don Archibald Armstrong [F&H].
1838		‘Paul Pry’ Oddities of London Life I 171: I’m splendaciously conwinced as it vos this here culprit as ‘boned the sifter’s grub’ last veek.
1844		Leeds Intelligencer 6 July 6: You should see what I hab bought, sich a splendacious particular walking stick.
1849		Bell’s Life in Sydney 17 Feb. 3/1: If Mir Mottram had not bin so werry impeterous that splendaclous tightner would have bin paid for.
1875		‘Aliph Cheem’ Lays of Ind (1905) 7: More splendaciously dressed / Less opaque than the rest.
1887		‘’Arry on Law & Order’ Punch 26 Nov. 249/1: A street rush is something splendacious to fellers of sperrit like me.
1894		S. Wales Echo 8 Dec. 4/1: ‘Oh, Crimey [...] didn’t it come off splendacious!’.
1913		E.L. Warnock ‘Terms of Approbation And Eulogy’ in DN IV:i 19: splendacious. Splendid. Facetious [...] ‘They live in a splendacious home’ [...] splendidious. [...] splendidous. [...] ‘Those flowers are splendidous.’.