bottom vs lake bed

bottom and lake bed both are nouns.

Word	Noun	Adjective	Verb	Adverb
bottom	Yes	Yes	Yes	No
lake bed	Yes	No	No	No

As nouns, lake bed is a hyponym of bottom; that is, lake bed is a word with a more specific, narrower meaning than bottom:

bottom (noun)	lake bed (noun)
a cargo ship	the bottom of a lake
the fleshy part of the human body that you sit on
the lower side of anything
the lowest part of anything
a depression forming the ground under a body of water
low-lying alluvial land near a river
the second half of an inning; while the home team is at bat

bottom (adjective)	lake bed (adjective)
situated at the bottom or lowest position
the lowest rank

bottom (verb)	lake bed (verb)
come to understand
strike the ground, as with a ship's bottom
provide with a bottom or a seat