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Obesophobia - Fear of gaining weight.(Pocrescophobia)
Ochlophobia - Fear of crowds or mobs.
Ochophobia - Fear of vehicles.
Octophobia - Fear of the figure 8.
Odontophobia - Fear of teeth or dental surgery.
Odynophobia or Odynephobia - Fear of pain. (Algophobia)
Oenophobia - Fear of wines.
Oikophobia - Fear of home surroundings, house.(Domatophobia, Eicophobia)
Olfactophobia - Fear of smells.
Ombrophobia - Fear of rain [...]