There is certainly a lot of them:
OD hypothetical force of natural power
OE Faroean wind
OF coming from
OH to exclaim “oh”
OM mantra used in meditation
ON side of wicket where cricket batsman stands
OP style of abstract art
OR heraldic color gold
OS orifice/bone/ridge of sand (esker)
OW intj. expressing sudden pain
OX hoofed mammal/clumsy person
OY intj. expressing dismay
from the Scrabble two-letter list.
It’s odd that OK is not on this list. It’s not an acronym. How about a poem using only these words? Golly, it’s pretty hard. Maybe if every other word was a two-letter word staring with o. So like, Oh, the ox said ow riding on a oe. I got lazy and didn’t bother finishing it with all the words.