stenography vs tachygraphy

stenography and tachygraphy both are nouns.

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

As nouns, stenography and tachygraphy are synonyms defined as:

stenography and tachygraphy: a method of writing rapidly using an abbreviated symbolic system

Other synonyms of stenography include shorthand.

stenography (noun)	tachygraphy (noun)
the act or art of writing in shorthand	a method of writing rapidly using an abbreviated symbolic system
a method of writing rapidly using an abbreviated symbolic system