The most common and most likely answer to this crossword clue is the 9 letter word BIGHEADED
I've seen this crossword clue in The Guardian
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A
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D
More clues leading to the result BIGHEADED
- Conceited editor to support significant source
- Egocentric British, stupid to give up power
- Arrogant tailor: he’d be glad, I being short of length
- Conceited and obstinate, wanting new leader
- Conceited, like Humpty Dumpty?
- Leader described by prominent journalist as ‘conceited’
- Falsely superior large loaf has seeds occasionally
Buddy explains!

The straight part
We know that "Falsely superior" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case falsely superior = bigheaded.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 BIGHEADED mean?
BIGHEADED adjective- Arrogant, having an exaggerated perception of one's positive qualities.