The Collaborative International Dictionary of English v.0.48:
Cheerfully \Cheer"ful*ly\, adv. In a cheerful manner, gladly. [1913 Webster]WordNet (r) 3.0 (2006):
cheerfully adv 1: in a cheerful manner; "he cheerfully agreed to do it" [ant: cheerlessly]The Jargon File (version 4.4.7, 29 Dec 2003):
cheerfully adv. See happily.