Strong's G884 — ἀχάριστος (adjective)
acharistos (ach-ar'-is-tos) adj.
1. thankless, i.e. ungrateful
[from G1 (as a negative particle) and a presumed derivative of G5483]
KJV: unthankful 
Root(s): G1, G5483 
Hebrew root: χαρίζομαι
Occurrences: 2