Green’s Dictionary of Slang

1. (US) precisely, exactly.

1844		‘Jonathan Slick’ High Life in N.Y. (1854) 228: We drew up co-wallop right afore Jase’s house.
1852		Congressional Globe 17 Aug. Appendix 959: He goes right kerwallop over into the Whig party, and nothing will content him but an appropriation of money.

2. indicating suddeness, or a fall.

1849		W.C. Hall ‘Mike Hooter’s Fight with the “Bar”’ Spirit of the Times 10 Nov. (N.Y.) 452: What? Didn’t he roll and wabble and play kerwallop ’mong those ar canes and briars?
1850		Keowee Courier (Pickens Court hse, SC) 26 Oct. 1/6: Preacher tried to pass Colt, and cowollop, crosh, cochunk! we all cum down like ’simmons arter frost.
1861		Sunbury American (PA) 26 Jan. 1/7: Down we went together in a pile, cowhallop on a big rock.
1871		Eaton Wkly Democrat (OH) 20 Apr. 2/3: You wriggle about like an eel [...] and you fall, cowhallop upon the broken glass bottles.
1886		Hartford Herald (KY) 14 July 3/4: Townsend [...] came down ‘kerwhallop’ on economical principles and the temperance side.
1902		W.N. Harben Abner Daniel 301: His hand run up an’ knocked me off’n the track kerwhallop.
1907		Wash. Post 12 July 6/7: Clash-Bang ! Bang-Clash! Kerwhallop-Sock!
1908		C. Fowler letter 5 Oct. in Tomlinson Rocky Mountain Sailor (1998) 335: [...] [W]e fetched up against the old tree kerwolop .
1909		Tacoma Times (WA) 25 Nov. 4/5: Tom Murchison raised that awful Turk’s sword and brought it down kerwollop—.
1957		Atchison (Kansas) Daily Globe 17 Nov. 3-A/5: Ten to one his heels fly up, and the heaviest part of his body [...] comes kerwhallop into the mud.