pho·tot·o·nus 
(fō-tŏtn-əs)
(fō-tŏtn-əs)n.
The state of being sensitive to or irritated by light.
pho′to·tonic (fō′tə-tŏnĭk) adj.
- opinion
- opinionate
- opinionated
- opinionatedly
- opinionative
- opinionatively
- opioid
- opisthobranch
- opisthognathism
- opisthognathous
- opium
- opium poppy
- Oporto
- opossum
- opossum shrimp
- Oppenheimer
- opponency
- opponent
- opportune
- opportunely
- opportuneness
- opportunism
- opportunist
- opportunistic
- opportunistic infection