Green’s Dictionary of Slang

ownio n.

In phrases

on one’s ownio (also on one’s owny-o) [cod Italian]

by oneself.

1946		(con. 1912) B. Marshall George Brown’s Schooldays 37: No sneaking down to the boiler and filling your filthy little pot all on your ownio.
1986–7		Maledicta IX 144: They may congregate in the Circus or certain pubs but usually work on their ownio (alone), a term none of them could trace back to the Victorian music-hall ditty, ‘Oh, oh, Antonio... left me on my ownio.’.
1999		(con. 1917) R. Doyle A Star Called Henry (2000) 198: You didn’t think I could let these bucks have a meeting all on their ownio, did you?