Partly open (4)
I believe the answer is:
ajar
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">partly open</span>' is the definition.<br/ ><span class="explanation-format__explanation">(as in a door which has been left ajar)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ajar that I've seen before include "near closing?" , "Fractionally open" , "Not to answer" , "It's nearly open" , "Not quite shut" .)