An act in which something is knocked on, or the sound thus produced(noun)
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Use "knocking" in a sentence
"By way, too, of further proof that my imagination had awakened, the significance of that knocking at the door set something vibrating within me that most surely had never vibrated before, so that I suddenly realized with what atmosphere of mystical suggestion is the mere act of knocking surrounded -- _knocking at a door_ -- both for him who knocks, wondering what shall be revealed on opening, and for him who stands within, waiting for the summons of the knocker."
"Gwynne had the title knocking around in his brain for years and didn't know what to do with it, until he passed it on to his IRONWEED costar."
"He will be under pressure next season to have the Bluejays again knocking on the NCAA tourney door after having their streak of 20 or more victories snapped at 11 straight seasons."