Rap
Part of speech: noun
Definition: A sharp blow with something hard. Blame (for something). Rap music.
Part of speech: verb
Definition: To strike something sharply with one's knuckles. To speak lyrics in the style of rap music.
Example sentence: I wrote 'Oath' for Cher Lloyd because there were really no best-friend anthems out there. Not only did she love it, she wanted me to rap on it, too!
Knock
Part of speech: noun
Definition: An abrupt rapping sound, as from an impact of a hard object against woodAn impact.a batsman's innings.A type of abnormal combustion occuring in spark ignition engines. Normally a flame front advances progressively out from the spark, but when knock occurs unburnt air/fuel ahead of the flame self-ignites under the heat and pressure, producing a characteristic knocking sound and a sudden further increase in pressure which can be very damaging to the engine.
Part of speech: verb
Definition: To rap one's knuckles against something, especially wood.To bump or impact.To denigrate, undervalue.
Example sentence: I'm not the greatest; I'm the double greatest. Not only do I knock 'em out, I pick the round.