The Collaborative International Dictionary of English v.0.48:
Solemnly \Sol"emn*ly\, adv. In a solemn manner; with gravity; seriously; formally. [1913 Webster] There in deaf murmurs solemnly are wise. --Dryden. [1913 Webster] I do solemnly assure the reader. --Swift. [1913 Webster]WordNet (r) 3.0 (2006):
solemnly adv 1: in a grave and sedate manner; "the judge sat there solemnly"