decree vs rule in

decree is a noun but rule in is not a noun.

Word	Noun	Adjective	Verb	Adverb
decree	Yes	No	Yes	No
rule in	No	No	Yes	No

As verbs, rule in is a hyponym of decree; that is, rule in is a word with a more specific, narrower meaning than decree:

decree: decide with authority
rule in: include or exclude by determining judicially or in agreement with rules

Other hyponyms of decree include override, overrule, overthrow, overturn, reverse, rule out.

decree (noun)	rule in (noun)
a legally binding command or decision entered on the court record (as if issued by a court or judge)

decree (verb)	rule in (verb)
decide with authority	include or exclude by determining judicially or in agreement with rules
issue a decree