Sees coils around a triangle (9)
I believe the answer is:
isosceles
'a triangle' is the definition.
(isosceles triangle is a kind of triangle)
'sees coils around' is the wordplay.
'around' is an anagram indicator.
'sees'+'coils'='seescoils'
'seescoils' with letters rearranged gives 'ISOSCELES'.
(Other definitions for isosceles that I've seen before include "(Of triangles) having two sides the same" , "Describing a triangle with two equal sides" , "Of triangular, with two sides of equal length" , "Kind of triangle" , "Triangle with two sides of equal length" .)