Retain; tower (4)
I believe the answer is:
keep
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">retain</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I know that retain can be written as keep)</span><br/ ><br/ >'<span class="explanation-format__original">tower</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for keep that I've seen before include "Conserve" , "Guard" , "Retain; part of castle" , "Save" , "Only one cricketer on field will" .)