All is inside whatever you think (5)
I believe the answer is:
every
'all' is the definition.
(similar in meaning)
'inside whatever you think' is the wordplay.
'inside' indicates the answer is hidden within the clue.
'EVERY' is hidden in the letters of 'whatever you think'.
'is' acts as a link.
(Other definitions for every that I've seen before include "As much as possible" , "'God bless us - - one !'" , "Each (one of a set)" , "The best possible" , "All, taken separately" .)