διαγωνίζεσθαι

From LSJ

πολλῶν ὁ καιρὸς γίγνεται διδάσκαλος → the critical moment will turn out to be the teacher of many things

Source

Greek > English (Woodhouse Verbs Reversed)

(see also διαγωνίζομαι): dispute

Lexicon Thucydideum

decertare, to fight decisively, 5.10.3, 8.46.2.
iure disceptare, to discuss according to right, 1.39.1.