Middle English word thanks comes from Proto-Indo-European *tong-

Detailed word origin of thanks

Dictionary entry	Language	Definition
*tong-	Proto-Indo-European (ine-pro)
*þankō	Proto-Germanic (gem-pro)
*þankōs	Proto-Germanic (gem-pro)
þancas	Old English (ang)
thankes	Middle English (enm)

Words with the same origin as thanks