Stabilising weight (7)
I believe the answer is:
ballast
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stabilising weight</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 ballast that I've seen before include "Steadying weight found at balls" , "Weight to stabilise a ship" , "Heavy material giving ship stability" , "Heavy material taken aboard to steady ship" , "Heavy material for steadying ship" .)