κρουστέον
From LSJ
Ὁ δὲ μὴ δυνάμενος κοινωνεῖν ἢ μηδὲν δεόμενος δι' αὐτάρκειαν οὐθὲν μέρος πόλεως, ὥστε ἢ θηρίον ἢ θεός → Whoever is incapable of associating, or has no need to because of self-sufficiency, is no part of a state; so he is either a beast or a god
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.