The Collaborative International Dictionary of English v.0.48:
Alliterative \Al*lit"er*a*tive\ (?; 277), a. Pertaining to, or characterized by, alliteration; as, alliterative poetry. -- Al*lit"er*a*tive*ly, adv. -- Al*lit"er*a*tive*ness, n. [1913 Webster]WordNet (r) 3.0 (2006):
alliteratively adv 1: in an alliterative manner; "the early Norse poets wrote alliteratively"