eucharisteo

εὐχαριστῶ [2 verses](1st sg pres ind act) "I thank" is from eucharisteo, which means "to bestow a favor on," "to oblige," "to be thankful," "to return thanks," and "to be received with thanks."  - The Greek word translated as "thank" means both to offer a favor and to be grateful for receiving favors. The two ideas were tied together. The idea is that bestowing a favor automatically creates thankfulness. This is related to the sense of "debt" in the Gospels, which is a topic Christ addresses more commonly, most noticeably in the Lord's Prayer.