Stuff in (4)
I believe the answer is:
cram
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stuff in</span>' is the definition.<br/ ><span class="explanation-format__explanation">(thesaurus)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cram that I've seen before include "Study hard for exam" , "Quickly learn - stuff" , "A crush" , "Swot (for exam)" , "jam" .)