The most common and most likely answer to this crossword clue is the 11 letter word PHILOSOPHER
P
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More clues leading to the result PHILOSOPHER
- His poor help upset Isaac Newton, perhaps
- Mill's thing for grinding? It's what many have sought
- A great thinker, hope Polish revolutionary overcomes Russian leader
- Pressure on Polish hero worried deep thinker
- Calm, rational type of duke presently leading men harbouring dashed hopes
- Greek character, see, with concessionary gift — offered to the female wisdom-seeker?
- His help with poor’s extraordinary, I think
- Boy of 11 — he’s poor, going astray, one thinks
Buddy explains!

The straight part
We know that "Calm, rational type" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case calm, rational type = philosopher.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 PHILOSOPHER mean?
PHILOSOPHER noun- A lover of wisdom.
- A student of philosophy.
- A scholar or expert engaged in or contributing to philosophical inquiry.
- A person who applies the principles of philosophy to the conduct of their life, as by acting calmly and rationally in the face of inevitable change.
- A student, scholar, or expert in any branch of knowledge, especially those branches studied prior to being considered part of pure science.
- An alchemist.