Holding tight, enter Tesla with Bluebird alongside (9)
I believe the answer is:
retention
'holding' is the definition.
(synonyms)
'tight enter tesla with bluebird alongside' is the wordplay.
'tight' is an anagram indicator (tight can mean drunk).
'tesla' becomes 'T' (scientific unit).
'with' is a charade indicator (letters next to each other).
'bluebird alongside' becomes 'ion' (I can't explain this - if you can you should give a lot more credence to this answer).
'enter' with letters rearranged gives 'reten'.
'reten'+'t'+'ion'='RETENTION'
Can you help me to learn more?
(Other definitions for retention that I've seen before include "memory" , "Failure to eliminate a substance from the body" , "Capacity to remember" , "Enter into custody" , "maintenance" .)