ink vs indelible ink

ink and indelible ink both are nouns.

Word	Noun	Adjective	Verb	Adverb
ink	Yes	No	Yes	No
indelible ink	Yes	No	No	No

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

Other hyponyms of ink include drawing ink, India ink, magnetic ink, printer's ink, printing ink, writing ink.

ink (noun)	indelible ink (noun)
dark protective fluid ejected into the water by cuttlefish and other cephalopods	ink that cannot be erased or washed away
a liquid used for printing or writing or drawing

ink (verb)	indelible ink (verb)
fill with ink
mark, coat, cover, or stain with ink
append one's signature to