thankful 2170 # eucharistos {yoo-khar'-is-tos}; from 2095 and a 
derivative of 5483; well favored, i.e. (by implication) grateful:
 -- {thankful}.[ql

thankfulness 2169 # eucharistia {yoo-khar-is-tee'-ah}; from 2170;
 gratitude; actively, grateful language (to God, as an act of 
worship): -- {thankfulness}, (giving of) thanks(-giving).[ql

unthankful 0884 # acharistos {ach-ar'-is-tos}; from 1 (as a 
negative particle) and a presumed derivative of 5483; thankless, 
i.e. ungrateful: -- {unthankful}.[ql