κρουστέον
From LSJ
Ἀναβάντα γὰρ εἰς τὴν ἀκρόπολιν, καὶ διὰ τὴν ὑπερβολὴν τῆς λύπης προσκόψαντα τῷ ζῆν, ἑαυτὸν κατακρημνίσαι → For he ascended the acropolis and then, because he was disgusted with life by reason of his excessive grief, cast himself down the height
English (LSJ)
A one must knock at, τηνδεδί (sc. θύραν) Ar.Ec.989.
Greek (Liddell-Scott)
κρουστέον: ῥημ. ἐπίθ., δεῖ κρούειν, τὴν θύραν Ἀριστοφ. Ἐκκλ. 989.
French (Bailly abrégé)
adj. verb. de κρούω.