Diffident or reticent (8)
I believe the answer is:
reserved
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">diffident</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(similar in meaning)</span><br/ ><br/ >'<span class="explanation-format__original">reticent</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ ></span>
(Other definitions for reserved that I've seen before include "Quiet, not given to showing emotion" , "cool" , "Shy; booked" , "Booked - reticent" , "Slow to show emotion" .)