Source : Webster's Revised Unabridged Dictionary (1913)

Epistolary \E*pis"to*la*ry\, a. [L. epistolaris, fr. epistola:
   cf. F. ['e]pistolaire.]
   1. Pertaining to epistles or letters; suitable to letters and
      correspondence; as, an epistolary style.

Source : WordNet®

epistolary
     adj : written in the form of or carried on by letters or
           correspondence; "an endless sequence of epistolary love
           affairs"; "the epistolatory novel" [syn: {epistolatory}]