The most common and most likely answer to this crossword clue is the 8 letter word STOICISM
I've seen this crossword clue in Financial Times
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More clues leading to the result STOICISM
Buddy explains!
The straight part
We know that "uncomplaining fortitude in suffering" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case uncomplaining fortitude in suffering = stoicism.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 STOICISM mean?
STOICISM noun- A school of philosophy popularized during the Roman Empire that emphasized reason as a means of understanding the natural state of things, or logos, and as a means of freeing oneself from emotional distress.
- A real or pretended indifference to pleasure or pain; insensibility; impassiveness.