Green’s Dictionary of Slang

(US) a large amount, e.g. a whole slather of pretty women; slathers of fresh fruit.

1871		L.H. Bagg Four Years at Yale 47: Slathers, an abundance, quantities, lots.
1876		‘Mark Twain’ Tom Sawyer 75: They get slathers of money—most a dollar a day.
1888		‘Mark Twain’ in New Princeton Rev. 50: Mr. [Newton] can repeat slathers and slathers of another man’s literature.
1899–1900		C.L. Cullen Tales of the Ex-Tanks 21: Never had such slathers of luck in my life.
1906		E. Dyson Fact’ry ’Ands 208: ‘Tribulation in ther ’appy ’ome?’ [...] ‘Slathers, Mills, old man.’.
1916		O.O. McIntyre New York Day By Day 31 Aug. [synd. col.] There may be slathers of actors who are more finished but Larry Comer appeals to me.
1920		F. Packard White Moll 216: There wasn’t anything said about the slather of gems that was the reward of heroism from a grateful nabob.
1953		Randolph & Wilson Down in the Holler 285: Them fellers has all got slathers of money.
1984		Clarion-Ledger (Jackson, MS) 25 Nov. 3/1: People who lounge around stroking [...] their calf muscles usually have slathers of money.