Formally prudish (4)
I believe the answer is:
prim
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">formally prudish</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 prim that I've seen before include "Old-maidish" , "Straitlaced and proper" , "Straight-laced" , "Affectedly dainty or refined" , "Schoolmarmish" .)