Rocket stage (7)
I believe the answer is:
booster
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">rocket stage</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 booster that I've seen before include "Additional strengthening dose" , "Space rocket's first stage" , "tonic" , "Additional dose that makes sure the first was effective" , "Additional dose to make sure the first one was effective" .)