Cause of worry or trouble (8)
I believe the answer is:
headache
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">cause of worry</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >'<span class="explanation-format__original">trouble</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ ></span>
(Other definitions for headache that I've seen before include "Problem, nuisance" , "Cause of worry or trouble" , "A pain in the brain" , "Worry, trouble (colloq.)" , "Pain in the cranium" .)