Extravagant academic left one opening (10)
I believe the answer is:
profligate
'extravagant' is the definition.
(I know that extravagant can be written as profligate)
'academic left one opening' is the wordplay.
'academic' becomes 'prof' (short for professor).
'left one opening' becomes 'ligate' (I can't explain this - if you can you should believe this answer much more).
'prof'+'ligate'='PROFLIGATE'
Can you help me to learn more?
(Other definitions for profligate that I've seen before include "Recklessly extravagant" , "Husband would not be" , "Debauched" , "Dissolute" , "Recklessly wasteful" .)