Guided round island, certainly having much free time (8)
I believe the answer is:
leisured
'having much free time' is the definition.
(I've seen this before)
'guided round island certainly' is the wordplay.
'guided' becomes 'led' ('lead' can be a synonym of 'guide').
'round' is an insertion indicator.
'island' becomes 'i'.
'certainly' becomes 'sure' ('sure' can be a synonym of 'certainly'**).
'i'+'sure'='isure'
'led' enclosing 'isure' is 'LEISURED'.
(Other definitions for leisured that I've seen before include "Having much free time" , "Having plenty of free time" , "Not needing to work" , "unhurried" .)