Middle English word o comes from Old English a-, Latin o (The name of the letter O. O! (vocative particle). Oh!.)

Detailed word origin of o

Dictionary entry	Language	Definition
a-	Old English (ang)	Forming words with the sense from, away, off, out, e.g. āniman.
o	Latin (lat)	The name of the letter O. O! (vocative particle). Oh!.
ō	Old English (ang)
oa	Middle English (enm)

Words with the same origin as o