Severely plain (7)
I believe the answer is:
austere
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">severely plain</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for austere that I've seen before include "Stark" , "'Spartan, simple (7)'" , "Stern, grave" , "Severe, lacking comforts" , "Stern, severe" .)