Bible Greek and Hebrew Dictionaries combined for Word Studies
Genesis Chapter 1
thankful 2170 # eucharistos {yoo-khar'-is-tos}; from 2095 and a derivative of 5483; well favored, i.e. (by implication) grateful: -- {thankful}.
unthankful 0884 # acharistos {ach-ar'-is-tos}; from 1 (as a negative particle) and a presumed derivative of 5483; thankless, i.e. ungrateful: -- {unthankful}.