O-hook (Ҩ ҩ) is a letter of the Cyrillic alphabet used in the Abkhaz language and placed between O and Π in the alphabet. This letter represents the labial-palatal approximant/ɥ/, the sound of u in Frenchluit. When romanized, it is written as an o with a small dot below the letter. It bears various similarities to the Greek letter theta (Θ θ).
Unicode
In the Unicode text-encoding standard, the letter is called CYRILLIC CAPITAL/SMALL LETTER ABKHASIAN HA and falls under the code points U+04A8 for a capital letter and U+04A9 for the small one. In the earlier Unicode version 1.0, the letters were called CYRILLIC CAPITAL/SMALL LETTER O HOOK.
References
Daniels, Peter D. The World's Writing Systems. Oxford University Press, 1996.