πρόθυμοςpróthymos

forward in spirit, i.e. predisposed; neuter (as noun) alacrity

Greek (New Testament) · G4289

Meanings

willing, ready: Matthew 26:41, Mark 14:38; neuter, τὸ π. = ἡ προθυμία (Thuc., and elsewhere, 3 Maccabees 5:26), οὕτως τὸ κατ’ ἐμὲ (= classical Greek τὸ ἐμὸν) π., Romans 1:15 (but see ICC, in l.).

Same root

πρόpró · G4253"fore", i.e. in front of, prior (figuratively, superior) to
θυμόςthymós · G2372passion (as if breathing hard)
προθυμίαprothymía · G4288predisposition, i.e. alacrity
προθύμωςprothýmōs · G4290with alacrity

Where it appears

Appears 3 times in the Bible.

Matthew 26:41 Keep watch and pray, so that you will not give in to temptation. For the spirit is willing, but the body is weak!”
Mark 14:38 Keep watch and pray, so that you will not give in to temptation. For the spirit is willing, but the body is weak.”
Romans 1:15 So I am eager to come to you in Rome, too, to preach the Good News.

Source: G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922), public domain.