11 traits, from Oath to Overflow.
Oath · Occult · Oil · Olfactory · Oni · Ooze · Open · Oracle · Orc · Oread · Overflow
Trait
Oaths add an additional tenet to your code. You can usually have only one feat with this trait.
Core Rulebook, page 109.
Trait
This magic comes from the occult tradition, calling upon bizarre and ephemeral mysteries. Anything with this trait is magical.
Core Rulebook, page 634. Reprinted in G&G.
Trait
Oils are magical gels, ointments, pastes, or salves that are typically applied to an object and are used up in the process.
Core Rulebook, page 634.
Trait
An olfactory effect can affect only creatures that can smell it. This applies only to olfactory parts of the effect, as determined by the GM.
Bestiary, page 168.
Trait
Oni are a family of fiends who dwell on the Material Plane and take monstrous forms based on humanoid shapes.
Bestiary 2, page 309.
Trait
Oozes are creatures with simple anatomies. They tend to have low mental ability scores and immunity to mental effects and precision damage.
Core Rulebook, page 634. Reprinted in B1, B2, SoM.
Trait
These maneuvers work only as the first salvo on your turn. You can use an open only if you haven't used an action with the attack or open trait yet this turn.
Core Rulebook, page 634.
Trait
This trait indicates abilities from the oracle class.
Advanced Player’s Guide, page 269.
Trait
A creature with this trait is a member of the orc ancestry. These green-skinned people tend to have darkvision. An ability with this trait can be used or selected only by orcs. An item with this trait is created and used by orcs.
Core Rulebook, page 634. Reprinted in B1.
Trait
Oreads are planar scions descended from shaitans.
Bestiary 2, page 309.
Trait
Powerful impulses temporarily overdraw the energy of your kinetic gate. When you use an impulse that has the overflow trait, your kinetic aura deactivates until you revitalize it (typically with Channel Elements). Extinguishing your element this severely is taxing, and consequently, you can use only one overflow impulse per round, even if you reactivate your kinetic gate.
Rage of Elements, page 15.