Definition of "oncet"
oncet
/ˈwʌn(t)st/
adverb
not comparable
(Southern US, South Midland US, nonstandard) Once.
Quotations
Why, Judith, Granny Peavey, our maw's mother, told us oncet about a dumb supper that her and two other gals made when she was but sixteen year old, and her sweetheart away from her in Virginny, and she didn't know whar he was at, an' they brought her tales agin him."
1908, Alice MacGowan, Judith of the Cumberlands