Concise Bible Dictionary:
In the Old Testament there are five Hebrew words so translated, signifying “to be right, proper, fit,” which do not call for remark. In the New Testament are
1. δεῖ, often translated “must” and “ought.” It “behooved” the father to make merry when the prodigal son returned (Luke 15:32). Sinners received the punishment that was “fit” (Rom. 1:27).
2. ἱκαυόω. The Christian is made “fit” to share the portion of the saints in light (Col. 1:12).
3. εὔχρηστος. By the Christian separating himself from the vessels to dishonor, he becomes a vessel to honor, sanctified, “serviceable” to the Master (2 Tim. 2:21).