conspiracy vs secret plan

conspiracy and secret plan both are nouns.

Word	Noun	Adjective	Verb	Adverb
conspiracy	Yes	No	No	No
secret plan	Yes	No	No	No

As nouns, secret plan is a hypernym of conspiracy; that is, secret plan is a word with a broader meaning than conspiracy:

conspiracy: a plot to carry out some harmful or illegal act (especially a political plot)
secret plan: a secret scheme to do something (especially something underhand or illegal)

Other hypernyms of conspiracy include game, plot.

conspiracy (noun)	secret plan (noun)
a plot to carry out some harmful or illegal act (especially a political plot)	a secret scheme to do something (especially something underhand or illegal)
a secret agreement between two or more people to perform an unlawful act
a group of conspirators banded together to achieve some harmful or illegal purpose