knock down vs beat

knock down is not a noun while beat is a noun.

Word	Noun	Adjective	Verb	Adverb
knock down	No	No	Yes	No
beat	Yes	Yes	Yes	No

As verbs, beat is a hypernym of knock down; that is, beat is a word with a broader meaning than knock down:

knock down (noun)	beat (noun)
	the act of beating to windward; sailing as close as possible to the direction from which the wind is blowing
	a stroke or blow
	a regular rate of repetition
	the basic rhythmic unit in a piece of music
	(prosody) the accent in a metrical foot of verse
	the rhythmic contraction and expansion of the arteries with each beat of the heart
	the sound of stroke or blow
	a regular route for a sentry or policeman
	a member of the beat generation; a nonconformist in dress and behavior
	a single pulsation of an oscillation produced by adding two waves of different frequencies; has a frequency equal to the difference between the two oscillations

knock down (adjective)	beat (adjective)
	very tired

knock down (verb)	beat (verb)
shatter as if by explosion	wear out completely
knock down with force	be a mystery or bewildering to
cause to come or go down	come out better in a competition, race, or conflict
	beat through cleverness and wit
	hit repeatedly
	give a beating to; subject to a beating, either as a punishment or as an act of aggression
	stir vigorously
	strike (a part of one's own body) repeatedly, as in great emotion or in accompaniment to music
	strike (water or bushes) repeatedly to rouse animals for hunting
	shape by beating
	make by pounding or trampling
	produce a rhythm by striking repeatedly
	move rhythmically
	sail with much tacking or with difficulty
	move with a flapping motion
	indicate by beating, as with the fingers or drumsticks
	move with a thrashing motion
	move with or as if with a regular alternating motion
	make a rhythmic sound
	make a sound like a clock or a timer
	glare or strike with great intensity
	avoid paying
	be superior