lightness vs highlight

lightness and highlight both are nouns.

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

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

lightness: the visual effect of illumination on objects or scenes as created in pictures
highlight: an area of lightness in a picture

Other hyponyms of lightness include aura, aureole, gloriole, glory, halo, nimbus, sunniness, highlighting, brightness.

lightness (noun)	highlight (noun)
the trait of being lighthearted and frivolous	an area of lightness in a picture
the visual effect of illumination on objects or scenes as created in pictures	the most interesting or memorable part
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

lightness (verb)	highlight (verb)
	apply a highlighter to one's cheeks or eyebrows in order to make them more prominent
	move into the foreground to make more visible or prominent