The most common and most likely answer to this crossword clue is the 9 letter word AUSTERITY
I've seen this crossword clue in The Times
A
U
S
T
E
R
I
T
Y
More clues leading to the result AUSTERITY
- Harshness of wind over town with a hundred fleeing
- The latter stages of Faust: her pity shows simplicity
- Close to broke in most of country — no alternative to Tory policy?
- Wind’s regularly wintry, displaying harshness
- I stay true, prepared for great self-denial
- Australia trip quietly put off yet to be arranged in spartan state
- Harsh condition in treaty with US I revised
- An American domain removing right orbanning luxury
- I stay true, manifesting ascetic quality
Buddy explains!

The straight part
We know that "simplicity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case simplicity = austerity.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 AUSTERITY mean?
AUSTERITY noun- Severity of manners or life; extreme rigor or strictness; harsh discipline.
- Freedom from adornment; plainness; severe simplicity.
- A policy of deficit-cutting, which by definition requires lower spending, higher taxes, or both.
- Sourness and harshness to the taste.