Source : Webster's Revised Unabridged Dictionary (1913)

Entity \En"ti*ty\, n.; pl. {Entities}. [LL. entitas, fr. L. ens,
   entis, thing, prop. p. pr. of esse to be: cf. F. entit['e].
   See {Essence}, {Is}.]
   A real being, whether in thought (as an ideal conception) or
   in fact; being; essence; existence.

         Self-subsisting entities, such as our own personality.
                                                  --Shairp.

         Fortune is no real entity, . . . but a mere relative
         signification.                           --Bentley.

Source : WordNet®

entity
     n : that which is perceived or known or inferred to have its own
         distinct existence (living or nonliving)