Minimum found inside simple as that (5)
I believe the answer is:
least
'minimum' is the definition.
(similar in meaning)
'inside simple as that' is the wordplay.
'inside' indicates the answer is hidden within the clue.
'LEAST' is hidden within 'simple as that'.
'found' acts as a link.
(Other definitions for least that I've seen before include "To the lowest degree" , "Of minimal significance" , "Opposite of most" , "Most insignificant" , "Lowest amount" .)