ESR vs electron spin resonance

ESR and electron spin resonance both are nouns.

Word	Noun	Adjective	Verb	Adverb
ESR	Yes	No	No	No
electron spin resonance	Yes	No	No	No

As nouns, ESR and electron spin resonance are synonyms defined as:

ESR and electron spin resonance: microwave spectroscopy in which there is resonant absorption of radiation by a paramagnet

Other synonyms of ESR include electron paramagnetic resonance.

ESR (noun)	electron spin resonance (noun)
microwave spectroscopy in which there is resonant absorption of radiation by a paramagnet	microwave spectroscopy in which there is resonant absorption of radiation by a paramagnet
the rate at which red blood cells settle out in a tube of blood under standardized conditions; a high rate usually indicates the presence of inflammation