lightness vs buoyancy

lightness and buoyancy both are nouns.

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

As nouns, buoyancy is a hyponym of lightness; that is, buoyancy is a word with a more specific, narrower meaning than lightness:

Other hyponyms of lightness include airiness.

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