The “Dinner Jacket” is what the English call the Tuxedo. Therefore, the “suit” is the dinner jacket and trousers together.
With black Tie events it’s crucial you understand why the rules are so important. The Black Tie (Tux/Dinner Suit, whatever) is a uniform. It is administered so rarely that the few times you are asked to do it, you should do it well. No peacocking allowed. The Dinner Suit isn’t about showing your personality, it’s about letting your actual personality show your personality without any pretense. Uniqueness is supposed to come about in the finer details.
Black Tie Rules
Shirts – should be white or a very pale blue. Do not choose colours
Velvet jackets are fine (not new, either). Vests should be included anyway, to cover the waist.
A dinner suit should ONLY be Double-Breasted or 3-piece. EVER. It’s a hard-and-fast rule.
Lapels should never be notched.
Cufflinks should not be quirky; no scrabble cufflinks here. Get something nice and unique, but NOT quirky.
Patent shoes are a rule, too. Not necessarily pointy. Don’t want to look like Krusty the Clown. They should always be black.
Now, adding a bow tie or a shawl lapel does not instantly make a black-tie outfit.