electric arc vs electric discharge

electric arc and electric discharge both are nouns.

Word	Noun	Adjective	Verb	Adverb
electric arc	Yes	No	No	No
electric discharge	Yes	No	No	No

As nouns, electric arc and electric discharge are synonyms defined as:

electric arc and electric discharge: electrical conduction through a gas in an applied electric field

Other synonyms of electric arc include arc, discharge, spark.

electric arc (noun)	electric discharge (noun)
electrical conduction through a gas in an applied electric field	electrical conduction through a gas in an applied electric field