From The Collaborative International Dictionary of English v.0.48 :
beltless \belt"less\ adj.
lacking a belt. beltless jackets are in this season belted
Syn: unbelted.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) :
beltless
adj 1: lacking a belt; "unbelted jackets are in this season"
[syn: unbelted, beltless] [ant: belted]