Fred stripped partner thoroughly (6)
I believe the answer is:
really
'thoroughly' is the definition.
'fred stripped partner' is the wordplay.
'stripped' says to take the centre (outside letters removed).
'partner' becomes 'ally' (I've seen this in another clue).
The middle letters of 'fred' are 're'.
're'+'ally'='REALLY'
(Other definitions for really that I've seen before include "Honestly, it's a fact" , "as a matter of fact" , "Indeed" , "Actually, truly" , "In truth - one may be surprised to say it" .)