Sophist from Civil Service touring ace Hebridean islands (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

CS (Civil Service) round or ‘touring’ A (ace) + UIST (Hebridean Islands – North and South Uist) – yet another new word for us but as we walked the Hebridean Way last year we were familiar with North and South Uist.