Opening bet (4)
I believe the answer is:
ante
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">opening bet</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for ante that I've seen before include "Prefix meaning before" , "expected from stake" , "Pre-deal stake" , "Pay" , "Fixed stake" .)