Stuart essentially is touring foremost island paradise (6)
I believe the answer is:
utopia
'paradise' is the definition.
(I've seen this before)
'stuart essentially is touring foremost island' is the wordplay.
'essentially' says to take the centre.
'is touring' means one lot of letters goes inside another (touring can mean going round).
'foremost' becomes 'top' (synonyms).
'island' becomes 'i' (geographical abbreviation).
The centre of 'stuart' is 'ua'.
'top'+'i'='topi'
'ua' enclosing 'topi' is 'UTOPIA'.
(Other definitions for utopia that I've seen before include "Sir Thomas Moore's perfect society" , "Ideal country" , "More's imaginary state" , "Thomas More's 1516 book about life on an imaginary island" , "Thomas More's perfect society" .)