Line touching a circle (7)
I believe the answer is:
tangent
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">line touching a circle</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 tangent that I've seen before include "Trig ratio" , "mostly irrelevant item" , "What people often go off at!" , "Straight line resting on a circle" , "Straight line that touches but does not intersect a curve" .)