electronic countermeasures vs ECM

electronic countermeasures and ECM both are nouns.

Word	Noun	Adjective	Verb	Adverb
electronic countermeasures	Yes	No	No	No
ECM	Yes	No	No	No

As nouns, electronic countermeasures and ECM are synonyms defined as:

electronic countermeasures and ECM: electronic warfare undertaken to prevent or reduce an enemy's effective use of the electromagnetic spectrum

electronic countermeasures (noun)	ECM (noun)
electronic warfare undertaken to prevent or reduce an enemy's effective use of the electromagnetic spectrum	electronic warfare undertaken to prevent or reduce an enemy's effective use of the electromagnetic spectrum