Unable to express oneself clearly (12)
I believe the answer is:
inarticulate
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">unable to express oneself clearly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for inarticulate that I've seen before include "incoherent" , "Not able to speak coherently" , "Unable to express oneself clearly" , "incapable of clear speech" , "Incomprehensible" .)