Sophist from Civil Service touring ace Hebridean islands (7)
I believe the answer is:
casuist
'sophist' is the definition.
(synonyms)
'civil service touring ace hebridean islands' is the wordplay.
'civil service' becomes 'CS' (abbreviation).
'touring' is an insertion indicator (tour can mean to go around).
'ace' becomes 'a' (abbreviation).
'hebridean islands' becomes 'Uist' (Uist is a group of Hebridean islands).
'cs' going around 'a' is 'cas'.
'cas'+'uist'='CASUIST'
'from' acts as a link.
(Other definitions for casuist that I've seen before include "fine debater" , "Theological hair-splitter" , "He uses clever but false reasoning on moral issues" , "One quibbles" .)