stain vs methylene blue

stain and methylene blue both are nouns.

Word	Noun	Adjective	Verb	Adverb
stain	Yes	No	Yes	No
methylene blue	Yes	No	No	No

As nouns, methylene blue is a hyponym of stain; that is, methylene blue is a word with a more specific, narrower meaning than stain:

stain: (microscopy) a dye or other coloring material that is used in microscopy to make structures visible
methylene blue: a dark green dye used as a stain, an antiseptic, a chemical indicator, and an antidote in cyanide poisoning

Other hyponyms of stain include crystal violet, gentian violet, methylthionine chloride, counterstain.

stain (noun)	methylene blue (noun)
an act that brings discredit to the person who does it	a dark green dye used as a stain, an antiseptic, a chemical indicator, and an antidote in cyanide poisoning
a soiled or discolored appearance
a symbol of disgrace or infamy
anything regarded as making something unclean
(microscopy) a dye or other coloring material that is used in microscopy to make structures visible

stain (verb)	methylene blue (verb)
produce or leave stains
color with a liquid dye or tint
color for microscopic study
make dirty or spotty, as by exposure to air; also used metaphorically