The most common and most likely answer to this crossword clue is the 10 letter word PROFLIGATE
I've seen this crossword clue in The Daily Telegraph
P
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More clues leading to the result PROFLIGATE
- Dissolute academic at contest, losing it
- Wasteful academic delayed welcoming soldier back
- Spendthrift set get 23 24 with 50% off
- Dissolute scholar, learner I punish at college
- Wildly extravagant design of fragile pot
- Fragile pot damaged with rake
- Debauched academic to get tied up
- Pet of a girl, perhaps, but recklessly extravagant
- Extravagant tip a golfer developed
- Debauched scholar, student I confine to college grounds
Buddy explains!

The straight part
We know that "Extravagant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extravagant = profligate.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 PROFLIGATE mean?
PROFLIGATE noun- An abandoned person; one openly and shamelessly vicious; a dissolute person.
- An overly wasteful or extravagant individual.
- To drive away; to overcome.
- Inclined to waste resources or behave extravagantly.
- Immoral; abandoned to vice.
- Overthrown, ruined.