κρουστέον
From LSJ
τὸ δὲ ποιεῖν ἄνευ νοῦ ἃ δοκεῖ καὶ σὺ ὁμολογεῖς κακὸν εἶναι: ἢ οὔ → but doing what one thinks fit without intelligence is—as you yourself admit, do you not?—an evil
English (LSJ)
one must knock at, τηνδεδί (sc. θύραν) Ar.Ec.989.
French (Bailly abrégé)
adj. verb. de κρούω.
Greek (Liddell-Scott)
κρουστέον: ῥημ. ἐπίθ., δεῖ κρούειν, τὴν θύραν Ἀριστοφ. Ἐκκλ. 989.
Russian (Dvoretsky)
κρουστέον: adj. verb. к κρούω.
Dutch (Woordenboekgrieks.nl)
κρουστέον, adj. verb. van κρούω, er moet gebeukt worden.