Sad or depressed (4)
I believe the answer is:
blue
<span class="explanation-format__ClueExplanation">I believe this clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">sad</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that sad can be written as blue)</span><br/ ><br/ >'<span class="explanation-format__original">depressed</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for blue that I've seen before include "Vulgar" , "Miserable; waste (money)" , "and 17 World's largest mammal" , "See 7 Across" , "Colour of depression" .)