Shoal (6)
(Other definitions for lour that I've seen before include "(Of sky) look dark" , "Threatening appearance" , "Look sullen - frown" , "Scowl, look dark and threatening" , "Appear sullen or threatening" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">shoal</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 reef that I've seen before include "Great Barrier formation?" , "Ridge of rock just below ocean surface" , "Reduce a sail's surface - shipping hazard" , "Sandbank" , "portion of sail" .)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">shoal</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for school that I've seen before include "Group of artists < in coach" , "Teach - fishes swimming" , "Forms" , "Where one teaches" , "Instruct" .)