megacycle vs megacycle per second

megacycle and megacycle per second both are nouns.

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

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

Other synonyms of megacycle include Mc, megahertz, MHz.

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