The most common and most likely answer to this crossword clue is the 7 letter word PROFUSE
I've seen this crossword clue in The Daily Telegraph
P
R
O
F
U
S
E
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 = profuse.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 PROFUSE mean?
PROFUSE verb- To pour out; to give or spend liberally; to lavish; to squander.
- In great quantity or abundance; liberal or generous to the point of excess.