The most common and most likely answer to this crossword clue is the 9 letter word BAROMETER
I've seen this crossword clue in The Times
B
A
R
O
M
E
T
E
R
More clues leading to the result BAROMETER
- Weather forecaster that can take the pressure?
- Cockney in smashing deal? It shows the pressure one's under
- Cockney in to cut deal, one predicting change
- Instrument changed from amber to red, briefly
- Remote working after lawyers showing indication of pressure
- Meteor crashes on line — it’ll take the pressure
- Indicator of change, portent endlessly disrupting trade
- One senses pressure to exchange Italian capital for roubles
- Confused Robert and me with a measuring instrument
- Indicator of change, sign mostly displayed in centre of trade
Buddy explains!

The straight part
We know that "It shows the pressure one's under" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it shows the pressure one's under = barometer.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 BAROMETER mean?
BAROMETER noun- An instrument for measuring atmospheric pressure.
- (by extension) Anything used as a gauge or indicator.