Hold onto (4)
I believe the answer is:
keep
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">hold onto</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 keep that I've seen before include "Retain in old castle (4)" , "Retain possession of" , "Stock" , "Retain; stronghold" , "Eg, beef" .)