Estimating (8)
I believe the answer is:
guessing
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">estimating</span>' is the definition.<br/ ><span class="explanation-format__explanation">('guess' can be a synonym of 'estimate')</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for guessing that I've seen before include "Reckoning, estimating" , "Supposing, estimating" , "'Conjecturing, surmising (8)'" , "Speculating, estimating" , "Reckoning, hazarding" .)