O.
- Omnigender - (adj.) - A nonbinary gender identity that describes people who experience all or many gender identities on the gender spectrum simultaneously or over time. Similar to pangender.
- Omnisexual - (adj.) - Relating to or being a person who experiences sexual attraction towards all genders.
- Oophorectomy - (n.) - Surgical removal of the ovaries.
- Orchiectomy - (n.) - Surgical removal of the testicles.
- Outing - (v.) - To reveal to that someone is transgender without consent of the trans person in question.
- Ovulation - (n.) - The phase of The Menstrual Cycle during which pregnancy is most likely to occur.