tachygraphy vs handwriting

tachygraphy and handwriting both are nouns.

Word	Noun	Adjective	Verb	Adverb
tachygraphy	Yes	No	No	No
handwriting	Yes	No	No	No

As nouns, handwriting is a hypernym of tachygraphy; that is, handwriting is a word with a broader meaning than tachygraphy:

tachygraphy: a method of writing rapidly using an abbreviated symbolic system
handwriting: something written by hand

Other hypernyms of tachygraphy include hand, script.

tachygraphy (noun)	handwriting (noun)
a method of writing rapidly using an abbreviated symbolic system	the activity of writing by hand
	something written by hand