Maybe the word is symmetrical or equilateral. Those are the only two I can think of which have 11 letters.
a shape with a line of symmetry
The 2D shape which has one line of symmetry is the trapezium.
An isosceles triangle has one line of symmetry
Not necessarily.
no
square
How about an isosceles triangle which has one line of symmetry
the shape is a heart.
An isosceles triangle and a kite have only one line of symmetry.
An isosceles triangle
symmetrical
Every right circular cone, conic section, and regular polygon has at least one line of symmetry.