To remember a Radian - Think radius and angle
It’s easy to remember what a radian is because it’s a combination of its name:
The name radian in sound emphasises that it is a raid (of a radius).
A radian is a radius on a circumference to give an angle.
A raid (radian) by a radius on a circumference.
When you talk about the radius of a circle you should recognise that it is closely coupled to a circumference.