The Greek adjective acharistos combines the negative particle a- and charis (grace, gratitude), meaning "without grace" in the relational sense — ungrateful, thankless, unappreciative. It appears twice in the New Testament: in Luke 6:35, where God is described as "kind to the ungrateful and wicked," and in 2 Timothy 3:2, in Paul's list of vices characterizing the last days.
The juxtaposition of acharistos with charis is theologically pointed. Ingratitude is the refusal of grace — the closing of one's hand against the gift. Paul's vice list in 2 Timothy 3 places ungrateful between "disobedient to their parents" and "unholy" — suggesting that the breakdown of gratitude to parents and to God is structurally similar. Jesus' teaching in Luke 6:35 is revolutionary: God extends kindness even to the ungrateful. This is the heart of grace — given not because we deserve it, but precisely because we don't.