The most common and most likely answer to this crossword clue is the 9 letter word MANDATORY
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The straight part
We know that "Required" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case required = mandatory.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.
What does MANDATORY mean?
MANDATORY noun- A sign or line that require the path of the disc to be above, below or to one side of it.
- A person, organisation or state who receives a mandate; a mandatary.
- Obligatory; required or commanded by authority.
- Of, being or relating to a mandate.