declaration vs dictum

declaration and dictum both are nouns.

Word	Noun	Adjective	Verb	Adverb
declaration	Yes	No	No	No
dictum	Yes	No	No	No

As nouns, dictum is a hyponym of declaration; that is, dictum is a word with a more specific, narrower meaning than declaration:

declaration (noun)	dictum (noun)
a statement that is emphatic and explicit (spoken or written)	an authoritative declaration
a formal expression by a meeting; agreed to by a vote	an opinion voiced by a judge on a point of law not directly bearing on the case in question and therefore not binding
(law) unsworn statement that can be admitted in evidence in a legal transaction
a formal public statement
(contract bridge) the highest bid becomes the contract setting the number of tricks that the bidder must make
a statement of taxable goods or of dutiable properties