Certainly, affirmative (3)
I believe the answer is:
yes
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">certainly</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(both can be used to answer in the affirmative)</span><br/ ><br/ >'<span class="explanation-format__original">affirmative</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(affirmative answer word)</span><br/ ><br/ ></span>
(Other definitions for yes that I've seen before include "I agree" , "Positive response" , "3 across" , "Pro vote" , "Positive reply" .)