Green’s Dictionary of Slang

1. artful, cunning, knowing; thus humgumption, a pretence of knowledge.

1818		‘Vocabulary’ in W. Perry London Guide ix: hum-gumption a pretending to the same [i.e. sharpness of perception].
1823		‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 101: A knowing sort of humbug is Humgumptious.

2. (US) fine, grand, pretentious.

1913

E.L. Warnock ‘Terms of Approbation And Eulogy’ in DN IV:i 18: humgumptious. Splendid, excellent, pretentious. [...] ‘They are humgumptious people.’.