grat·is 
(grătĭs, grätĭs, grā-)
(grătĭs, grätĭs, grā-)adv. & adj.
Without payment or charge.
[Middle English, from Latin grātīs, alteration of grātiīs, out of kindness, free, ablative pl. of grātia, kindness; see gwerə-2 in the Appendix of Indo-European roots.]