nok (krouo): The oriental house was fitted with heavy doors which were bolted and locked with wooden keys too large to be carried about, so that even a member of the household could not secure entrance until in response to his knock or call the door should be opened by someone within. At night the delay would be increased by the difficulty of arousing the inmates sleeping within the inner chambers. To persons familiar with such experiences, the words of Jesus concerning a higher entrance, "Knock, and it shall be opened unto you" (Mt 7:7; Lu 12:36), would have a unique force not easy for us to appreciate.
⇒See the definition of knock in the KJV Dictionary
Russell Benjamin Miller