Reticent, secretive (5-6)
I believe the answer is:
tight-lipped
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">reticent</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >'<span class="explanation-format__original">secretive</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for tight-lipped that I've seen before include "Determinedly reticent" , "Uncommunicative" , "Taciturn" .)