Posh knighted actor keeps money essentially in safe (6)
I believe the answer is:
unhurt
'safe' is the definition.
(similar in meaning)
'posh knighted actor keeps money essentially in' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'knighted actor' becomes 'hurt' (I can't explain this - if you can you should believe this answer much more).
'keeps money' becomes 'banks' ('bank' can be a synonym of 'keep money').
'essentially' means to look at the middle letters.
'in' is an insertion indicator.
The middle of 'banks' is 'n'.
'u'+'hurt'='uhurt'
'uhurt' enclosing 'n' is 'UNHURT'.
Can you help me to learn more?
(Other definitions for unhurt that I've seen before include "Free from injury" , "Safe and sound" , "Not damaged" , "Not injured or maimed" , "Lacking injury" .)