The Collaborative International Dictionary of English v.0.48:
Believing \Be*liev"ing\, a. That believes; having belief. -- Be*liev"ing*ly, adv. [1913 Webster]WordNet (r) 3.0 (2006):
believingly adv 1: in a credulous manner; "the children followed the teacher credulously" [syn: credulously, believingly] [ant: disbelievingly, incredulously, unbelievingly]