Green’s Dictionary of Slang

ownsome n.

In phrases

on one’s ownsome

by oneself.

1909		Modern Man 27 Nov. 12/1: [I]t struck me that there was no sound reason why I should let the rain spoil my holiday, and I made up my mind to go off to Oxford on my ownsome.
1946		Mezzrow & Wolfe Really the Blues 196: All on his ownsome, separated by an ocean from the battlefield of jazz.
1988		J.W. Warden Wayward Legionnaire 114: [O]ne eight-man tent standing all on its ownsome .