grateful (adj.)youdaoicibaDictYouDict[grateful 词源字典]
1550s, "pleasing to the mind," also "full of gratitude, disposed to repay favors bestowed," from obsolete adjective grate "agreeable, pleasant," from Latin gratus "pleasing" (see grace (n.)). "A most unusual formation" [Weekley]. Is there another case where English uses -ful to make an adjective from an adjective? Related: Gratefully (1540s); gratefulness.
Grateful often expresses the feeling and the readiness to manifest the feeling by acts, even a long time after the rendering of the favor; thankful refers rather to the immediate acknowledgment of the favor by words. [Century Dictionary]
[grateful etymology, grateful origin, 英语词源]
ungrateful (adj.)youdaoicibaDictYouDict
1550s, from un- (1) "not" + grateful. Related: Ungratefully.