The Collaborative International Dictionary of English v.0.48:

Exhortative \Ex*hor"ta*tive\, a. [L. exhortativus: cf. F.
   exhortatif.]
   Serving to exhort; exhortatory; hortative. --Barrow.
   [1913 Webster]

WordNet (r) 3.0 (2006):

exhortative
    adj 1: giving strong encouragement [syn: exhortative,
           exhortatory, hortative, hortatory]