Prohibit, legally (5)
I believe the answer is:
estop
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prohibit legally</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for estop that I've seen before include "Legal term" , "Legally hinder removal" , "Preclude certain evidence (at law) - bar (archaic)" , "Legally bar" , "Legally check" .)