The Collaborative International Dictionary of English v.0.48:

phobia \pho"bi*a\ (f[=o]"b[-e]*[.a]) n.
   Any irrational and persistent fear, whether of a situation,
   activity, or object; a phobia typically leads to a strong
   desire to avoid the object of the phobia.

   Syn: phobic disorder, phobic neurosis.
        [PJC]

The Collaborative International Dictionary of English v.0.48:

-phobia \-pho"bi*a\ (f[=o]"b[-e]*[.a]) suffix
   A combining form used as a suffix to designate specific
   phobias, such as agoraphobia (fear of public places),
   acrophobia (fear of heights). The first part of the combining
   form is usually derived from Greek.
   [PJC]

WordNet (r) 3.0 (2006):

phobia
    n 1: an anxiety disorder characterized by extreme and irrational
         fear of simple things or social situations; "phobic
         disorder is a general term for all phobias" [syn: phobia,
         phobic disorder, phobic neurosis]