An outside line to ring (7)
I believe the answer is:
'an outside line' is the definition.
'tangent' can be an answer for 'line' (tangent is a kind of line). I am not sure about the 'an outside' bit.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tangent that I've seen before include "Straight line resting on a circle" , "Geometric line" , "Completely different line of thought - trigonometrical function" , "A new line of thought" , "Particular line" .)