used to express a range of emotions including surprise, anger, disappointment, or joy, or when reacting to a remark

‘Oh no,’ said Daisy, appalled

Me? Oh, I'm fine

oh, shut up

Ohio (in official postal use)

a person's wife, husband, or partner (particularly used in online forums)

I often go to gigs on my own as my OH doesn't have the same musical tastes as me

the fifteenth letter of the alphabet

nought or zero (in a sequence of numerals, especially when spoken)

two seven o seven point six

a shape like that of a capital O; a circle

he made an O with his mouth