softener vs plasticiser

softener and plasticiser both are nouns.

Word	Noun	Adjective	Verb	Adverb
softener	Yes	No	No	No
plasticiser	Yes	No	No	No

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

softener: a substance added to another to make it less hard
plasticiser: a substance added to plastics or other materials to make them more pliable

Other hyponyms of softener include conditioner, plasticizer, water softener.

softener (noun)	plasticiser (noun)
a substance added to another to make it less hard	a substance added to plastics or other materials to make them more pliable