'Costless' definitions:

Definition of 'costless'

From: WordNet
adjective
Costing nothing; "complimentary tickets"; "free admission" [syn: complimentary, costless, free, gratis(p), gratuitous]

Definition of 'Costless'

From: GCIDE
  • Costless \Cost"less\ (k?st"l?s; 115), a. Costing nothing. [1913 Webster]