Edge with radius one metre (3)
I believe the answer is:
rim
'edge' is the definition.
(I know that rim is a type of edge)
'with radius one metre' is the wordplay.
'with' says to put letters next to each other.
'radius' becomes 'r' (abbreviation in geometry).
'one' becomes 'i' (Roman numeral).
'metre' becomes 'm' (synonyms).
'r'+'i' is 'ri'.
'ri'+'m'='RIM'
(Other definitions for rim that I've seen before include "Top edge" , "Outer edge of a wheel" , "Circular outer edge" , "Edge - lip" , "Circumference" .)