κρούω
1. "to strike, smite: to strike" one "against" another, κρ. χεῖρας "to clap" hands, Eur.; κρ. τὰ ὅπλα πρὸς ἄλληλα Thuc., etc.:— κρ. τὸν πόδα (i. e. κρ. τὴν γῆν τῶι ποδί) in dancing, Eur.
2. κέραμον κρούειν "to tap" an earthen vessel, to try whether it rings sound: hence "to examine, prove", Plat.
3. "to strike" a lyre with the plectron, id=Plat.
4. κρούειν τὴν θύραν "to knock at" the door "on the outside", Xen., etc.
5. as a nautical term, in Mid., κρούεσθαι πρύμναν, like ἀνακρούεσθαι, "to back" a ship, Thuc.