marker vs highlighter

marker and highlighter both are nouns.

Word	Noun	Adjective	Verb	Adverb
marker	Yes	No	No	No
highlighter	Yes	No	No	No

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

marker (noun)	highlighter (noun)
some conspicuous object used to distinguish or mark something	a fluorescent marker used to mark important passages in a text
a writing implement for making a mark	a cosmetic used to highlight the eyes or cheekbones
a distinguishing symbol