The Collaborative International Dictionary of English v.0.48:

Gruntle \Grun"tle\ (gr[u^]n"t'l), v. i. [Freq. of grunt.]
   To grunt; to grunt repeatedly. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

gruntle
    v 1: cause to be more favorably inclined; gain the good will of;
         "She managed to mollify the angry customer" [syn: pacify,
         lenify, conciliate, assuage, appease, mollify,
         placate, gentle, gruntle]