tachometer vs tach

tachometer and tach both are nouns.

Word	Noun	Adjective	Verb	Adverb
tachometer	Yes	No	No	No
tach	Yes	No	No	No

As nouns, tachometer and tach are synonyms defined as:

tachometer and tach: measuring instrument for indicating speed of rotation

tachometer (noun)	tach (noun)
measuring instrument for indicating speed of rotation	measuring instrument for indicating speed of rotation