πρόθυμον

From LSJ

ὃ γὰρ βούλεται, τοῦθ' ἕκαστος καὶ οἴεται → what he wishes to be true, each person also believes to be true | what he wishes, each person also believes

Source

Russian (Dvoretsky)

πρόθῡμον: τό Eur., Plat., NT = προθυμία.