The Collaborative International Dictionary of English v.0.48:

Supplicatory \Sup"pli*ca*to*ry\, a. [Cf. F. supplicatoire.]
   Containing supplication; humble; earnest.
   [1913 Webster]

WordNet (r) 3.0 (2006):

supplicatory
    adj 1: humbly entreating; "a suppliant sinner seeking
           forgiveness" [syn: suppliant, supplicant,
           supplicatory]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "supplicatory":
   adorant, adoring, begging, cadging, devotional, devout, imploring,
   in the dust, mendicant, mooching, on bended knee, petitionary,
   prayerful, precative, precatory, prostrate before, reverent,
   reverential, scrounging, solemn, suppliant, supplicant,
   supplicating, venerational, venerative, worshipful, worshiping