The most common and most likely answer to this crossword clue is the 8 letter word RUDIMENT
I've seen this crossword clue in The Guardian
R
U
D
I
M
E
N
T
More clues leading to the result RUDIMENT
- Weakling must have very little money in principle
- Basic uniform, grey, and split skirts
- Essential money to feed diminutive sort
- It could be true, mind shows undeveloped part
- Weakling keeps small coin of necessity
- Basic uniform, grey, and torn dresses
- Basic principle this person’s found in harsh holy books
- Basic uniform, stupid to get torn outside
- Beginning game, I’m hugged by lady with dictionary
- … I’m turned out by first principle
Buddy explains!

The straight part
We know that "necessity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case necessity = rudiment.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 RUDIMENT mean?
RUDIMENT noun- (often in the plural) A fundamental principle or skill, especially in a field of learning.
- (often in the plural) Something in an undeveloped form.
- A body part that no longer has a function
- In percussion, one of a selection of basic drum patterns learned as an exercise.
- To ground; to settle in first principles.