ligature vs grapheme

ligature and grapheme both are nouns.

Word	Noun	Adjective	Verb	Adverb
ligature	Yes	No	No	No
grapheme	Yes	No	No	No

As nouns, grapheme is a hypernym of ligature; that is, grapheme is a word with a broader meaning than ligature:

Other hypernyms of ligature include character, graph, graphic symbol.

ligature (noun)	grapheme (noun)
the act of tying or binding things together	a written symbol that is used to represent speech
something used to tie or bind
thread used by surgeons to bind a vessel (as to constrict the flow of blood)
a metal band used to attach a reed to the mouthpiece of a clarinet or saxophone
(music) a group of notes connected by a slur
character consisting of two or more letters combined into one