dictum vs legal opinion

dictum and legal opinion both are nouns.

Word	Noun	Adjective	Verb	Adverb
dictum	Yes	No	No	No
legal opinion	Yes	No	No	No

As nouns, legal opinion is a hypernym of dictum; that is, legal opinion is a word with a broader meaning than dictum:

dictum: an opinion voiced by a judge on a point of law not directly bearing on the case in question and therefore not binding
legal opinion: the legal document stating the reasons for a judicial decision

Other hypernyms of dictum include judgement, judgment, opinion.

dictum (noun)	legal opinion (noun)
an authoritative declaration	the legal document stating the reasons for a judicial decision
an opinion voiced by a judge on a point of law not directly bearing on the case in question and therefore not binding