This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 弙 is uncertain. It visually combines 弓 (bow) with 于, but the original semantic and phonetic roles are unclear.
With 弓 (bow) on the left and 于 on the right, imagine a bow being held or drawn, but the exact meaning is unclear.
For オ, picture an archer saying 'Oh!' as they draw the bow: Oh -> オ.