buoyancy vs lightness

buoyancy and lightness both are nouns.

Word	Noun	Adjective	Verb	Adverb
buoyancy	Yes	No	No	No
lightness	Yes	No	No	No

As nouns, lightness is a hypernym of buoyancy; that is, lightness is a word with a broader meaning than buoyancy:

Other hypernyms of buoyancy include weightlessness.

buoyancy (noun)	lightness (noun)
the property of something weightless and insubstantial	the trait of being lighthearted and frivolous
irrepressible liveliness and good spirit	the visual effect of illumination on objects or scenes as created in pictures
the tendency to float in water or other liquid	the property of being comparatively small in weight
cheerfulness that bubbles to the surface	having a light color
	the gracefulness of a person or animal that is quick and nimble
	a feeling of joy and pride