Line in geometry (3)
I believe the answer is:
ray
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">line in geometry</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 ray that I've seen before include "Beam or flatfish" , "Narrow beam of light" , "Gleam" , "A little light" , "Beam; man's name" .)