Phlegmatic (6)
I believe the answer is:
stolid
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">phlegmatic</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for stolid that I've seen before include "cool" , "Not excitable, unemotional" , "'Calm and dependable, showing little emotion (6)'" , "Showing little or no interest or emotion" , "Difficult to excite, apathetic" .)