κρουστέον
From LSJ
Dante Alighieri, Paradiso, XXXIII, v. 145
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.