The Collaborative International Dictionary of English v.0.48:

Odd Fellow \Odd" Fel`low\
   A member of a secret order, or fraternity, styled the
   Independent Order of Odd Fellows, established for mutual aid
   and social enjoyment.
   [1913 Webster]

WordNet (r) 3.0 (2006):

odd fellow
    n 1: someone regarded as eccentric or crazy and standing out
         from a group [syn: kook, odd fellow, odd fish, queer
         bird, queer duck, odd man out]