The most common and most likely answer to this crossword clue is the 9 letter word LANDGRAVE
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The straight part
We know that "nobleman" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nobleman = landgrave.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 LANDGRAVE mean?
LANDGRAVE noun- Specific nobiliary title ranking as count in certain feudal countships in the Holy Roman Empire, in present Germany.
- County nobleman in the British, privately held North American colony Carolina, ranking just below the proprietary (chartered equivalent of a royal vassal).