megahertz vs megacycle per second

megahertz and megacycle per second both are nouns.

Word	Noun	Adjective	Verb	Adverb
megahertz	Yes	No	No	No
megacycle per second	Yes	No	No	No

As nouns, megahertz and megacycle per second are synonyms defined as:

Other synonyms of megahertz include Mc, megacycle, MHz.

megahertz (noun)	megacycle per second (noun)
one million periods per second	one million periods per second