The most common and most likely answer to this crossword clue is the 2 plus 7 letter word DE RIGUEUR
I've seen this crossword clue in The Daily Telegraph
D
E
R
I
G
U
E
U
R
More clues leading to the result DE RIGUEUR
- I urged Europe, not half, to change — it's obligatory
- River Ure guide undergoes training, as is proper
- New guide about royal city of old required
- Obligatory EU guide revised with rights
- I’d urge breaking with Europe, as fashion dictates
- Terribly rude urge I suppressed, as required by etiquette
- Awfully rude urge I suppressed, as required by etiquette
Buddy explains!
The straight part
We know that "as required by etiquette" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as required by etiquette = de rigueur.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.