κρουστέον
From LSJ
Δύο γὰρ, ἐπιστήμη τε καὶ δόξα, ὧν τὸ μὲν ἐπίστασθαι ποιέει, τὸ δὲ ἀγνοεῖν → Two different things are science and belief: the one brings knowledge, the other ignorance
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.
Russian (Dvoretsky)
κρουστέον: adj. verb. к κρούω.
Dutch (Woordenboekgrieks.nl)
κρουστέον, adj. verb. van κρούω, er moet gebeukt worden.