hanky vs piece of material

hanky and piece of material both are nouns.

Word	Noun	Adjective	Verb	Adverb
hanky	Yes	No	No	No
piece of material	Yes	No	No	No

As nouns, piece of material is a hypernym of hanky; that is, piece of material is a word with a broader meaning than hanky:

hanky: a square piece of cloth used for wiping the eyes or nose or as a costume accessory
piece of material: a separate part consisting of fabric

Other hypernyms of hanky include piece of cloth.

hanky (noun)	piece of material (noun)
a square piece of cloth used for wiping the eyes or nose or as a costume accessory	a separate part consisting of fabric