Cancer or Capricorn (6)
I believe the answer is:
tropic
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">cancer or capricorn</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tropic that I've seen before include "Either that of Capricorn or Cancer" , "Line of latitude determined by the solstice" , "One of two parallels north and south of the equator" , "Parallel of latitude about 25o N or S" , "Capricorn, perhaps" .)