thanks n.

Old English þancian, þoncian "to give thanks, thank, to recompense, to reward," from Proto-Germanic *thankōjanan (source also of Old Saxon thancon, Old Norse þakka, Danish takke, Old Frisian thankia, Old High German danchon, Middle Dutch, Dutch, German danken "to thank"), from *thankoz "thought; gratitude," from PIE root *tong- "to think, feel."

It is related phonetically to think as song is to sing; for sense evolution, compare Old High German minna "loving memory," originally "memory." Also compare related Old English noun þanc, þonc, originally "thought," but also "good thoughts, gratitude." In ironical use, "to blame," from 1550s. To thank (someone) for nothing is recorded from 1703. Related: Thanked; thanking.

also pick-thank, c. 1500, "an officious fellow who does what he is not asked to do for the sake of gaining favor, a parasite or toady," from phrase pick thanks "procure consideration or favor by servile or underhanded means" (early 15c.); see pick (v.) + thanks.

1530s, "the giving of thanks," from thanks (n.) + present participle of give (v.). In the specific sense of "public celebration acknowledging divine favors" thanksgiving dates from 1630s (the first one in America was held October 1621 by Plymouth Colony Pilgrims in appreciation of assistance from members of the Massasoit tribe and celebration of the first harvest); though Thanksgiving Day itself is not attested until 1670s.