S/N vs signal/noise ratio

S/N and signal/noise ratio both are nouns.

Word	Noun	Adjective	Verb	Adverb
S/N	Yes	No	No	No
signal/noise ratio	Yes	No	No	No

As nouns, S/N and signal/noise ratio are synonyms defined as:

S/N and signal/noise ratio: the ratio of signal intensity to noise intensity

Other synonyms of S/N include signal/noise, signal-to-noise, signal-to-noise ratio.

S/N (noun)	signal/noise ratio (noun)
the ratio of signal intensity to noise intensity	the ratio of signal intensity to noise intensity