Where does “unthankful” come from?

Unthankful comes from Old English unþancfull, a compound of un- and þancfull, meaning not grateful or not thankful.

unthankful (English): Not thankful; ungrateful

Definitions

Step	Language	Word	Meaning
1	Middle English	unthankful	—
2	Old English	unþancful	—

unthankful — Etymology, Origin & Word History | Etymology Explorer