One sentence, said by someone who is allowed to say it, and then left standing. The Latin dictum simply means "a thing said". A useful picture: a line lifted out of a longer speech or judgment and set down on its own — short enough to quote, and firm enough that people repeat it instead of arguing with it.
Latin dictum, "a thing said", is the neuter past participle of dico, to say. Spanish dicho, a saying, comes from the same place. The English word keeps both halves of that: something said, and something now finished and quotable.
拉丁文 dictum 是動詞 dico（說）的過去分詞形，意思就是「被說出來的東西」；西班牙文的 dicho（諺語）也是同一條線。英文把兩層都留下來了：一句話被說出口，而且已經說完、定型，可以被別人整句搬走。
Wiktionary entry for dictum, etymology section, as supplied in this packet (source_ref kaikki:3f6f69a190036ae4:636734137)
Two branches
被當成定論的一句話
這一組就是核心畫面本身，兩個意思只是看向不同的地方：一個看說話的人，一個看那句話。
noun · C2
A dictum is a short, firm statement of opinion from someone whose word carries weight — a judge, a professor, an editor, the founder of a company. It is put forward as settled rather than as one view among several, and other people then repeat it as if it decides the matter.
權威之言；斷語
法庭上順帶說的話
法律把同一個畫面拿去做更細的分辨：判決裡哪些話是非講不可的，哪些只是順帶講的。順帶講的那些仍然是「說出來的一句話」，只是特別標明它不拘束後來的法院。
noun · C2
In law, a dictum is a remark a judge makes in a judgment that was not needed to decide the case. Because the case did not turn on it, later courts do not have to follow it, although they often quote it. The fuller Latin name is obiter dictum, and it is set against the part of the judgment that does bind later courts.
附帶意見（法律）
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
dictumnoun/ˈdɪk.təm/
An authoritative statement; a dogmatic saying; a maxim, an apothegm.
A judicial opinion expressed by judges on points that do not necessarily arise in the case, and are not involved in it.
The report of a judgment made by one of the judges who has given it.
An arbitrament or award.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。