Trouble of small island accommodating large fellows (7)
I believe the answer is:
ailment
'trouble' is the definition.
(thesaurus)
'small island accommodating large fellows' is the wordplay.
'small island' becomes 'ait' (an ait is a small island in a river).
'accommodating' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'fellows' becomes 'men' (fellow can mean a man).
'l'+'men'='lmen'
'ait' enclosing 'lmen' is 'AILMENT'.
'of' is the link.
(Other definitions for ailment that I've seen before include "Tummy upset, for instance" , "Complaint, affliction" , "Tim Alen has an odd indisposition." , "problem" , "Bodily disorder or disease" .)