beat vs knock down

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

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

As verbs, knock down is a hyponym of beat; that is, knock down is a word with a more specific, narrower meaning than beat:

Other hyponyms of beat include full, beat, beetle, bastinado, coldcock, deck, dump, floor, whang, paste, thrash, thresh, hammer.

beat (noun)	knock down (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

beat (adjective)	knock down (adjective)
very tired

beat (verb)	knock down (verb)
wear out completely	shatter as if by explosion
be a mystery or bewildering to	knock down with force
come out better in a competition, race, or conflict	cause to come or go down
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