weightlessness vs lightness

weightlessness and lightness both are nouns.

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

As nouns, weightlessness and lightness are synonyms defined as:

weightlessness and lightness: the property of being comparatively small in weight

weightlessness (noun)	lightness (noun)
the property of being comparatively small in weight	the trait of being lighthearted and frivolous
	the visual effect of illumination on objects or scenes as created in pictures
	the property of being comparatively small in weight
	having a light color
	the gracefulness of a person or animal that is quick and nimble
	a feeling of joy and pride