Cryptic crossword clue
Strength to take a seat, over 90 outside 9

The most common and most likely answer to this crossword clue is the 9 letter word INTENSITY

I've seen this crossword clue in The Guardian
I
N
T
E
N
S
I
T
Y

Buddy explains!

The straight part
We know that "Strength" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case strength = intensity.
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 INTENSITY mean?

INTENSITY noun
  1. The quality of being intense.
  2. The degree of strength.
  3. Time-averaged energy flux (the ratio of average power to the area through which the power "flows"); irradiance.
  4. Can mean any of radiant intensity, luminous intensity or irradiance.
  5. The severity of an earthquake in terms of its effects on the earth's surface, and buildings. The value depends on the distance from the epicentre, and is not to be confused with the magnitude.
INTENSITY noun
  1. The quality of being radiant, shining, bright or splendid.
  2. The flux of radiation emitted per unit solid angle in a given direction by a unit area of a source.

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