The most common and most likely answer to this crossword clue is the 7 letter word NEEDFUL
I've seen this crossword clue in The Times
N
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More clues leading to the result NEEDFUL
- Essential Tyneside editor gets flu treated
- End fuel supply that's essential
- Nude left almost shivering — what’s required?
- Required amount in syringe, ignoring foreign article
- Injection, perhaps, to remove foreign article necessary
- Vital contribution from knock-kneed full-back
- Eden shaking with flu, craving affection?
- They say massage before flu treatment is essential
- Required, once head of Hull, to make every second count
- Dancing nude with elf, it’s essential
Buddy explains!

The straight part
We know that "necessary" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case necessary = needful.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 NEEDFUL mean?
NEEDFUL noun- Ready money; wherewithal.
- Anything necessary or requisite.
- Needed; necessary; mandatory; requisite; indispensible.
- Needy; in need.