Prophēteuō (προφητεύω) means to prophesy — to speak forth a message from God. From pro (before/forth) + phēmi (to speak). The verb encompasses both foretelling (predicting) and forthtelling (proclaiming God's word to the present situation).
Prophecy in the NT is a gift of the Spirit (1 Cor. 12:10; 14:1-5) given for the building up of the church — not primarily for prediction but for strengthening, encouraging, and comfort (1 Cor. 14:3). Paul says "eagerly desire to prophesy" — it is the most valuable of speech gifts because it communicates directly to the assembled community. The prophetic tradition stretches from Moses ("would that all the LORD's people were prophets!" Num. 11:29) through Joel ("your sons and daughters will prophesy," Joel 2:28, quoted at Pentecost, Acts 2:17). Jesus himself prophēteuō-ed — and was rejected for it. The NT also warns of false prophets (Matt. 7:15) — those who speak in Jesus' name but lead astray.
The pro- prefix in Greek prophecy words is ambiguous: it can mean "before" (temporally) or "forth" (spatially). Most NT prophetic speech is "forthtelling" — speaking God's word into the present — with the predictive element secondary. 1 Corinthians 14 is the NT's most extensive teaching on prophetic practice: it is spoken, intelligible, ordered, and subject to evaluation. The Spirit's gift is not unaccountable; prophecy is tested.