Use mathematical instrument to plant a quadrangle (3,6)
I believe the answer is:
set square
'use mathematical instrument' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'plant a quadrangle' is the wordplay.
'plant' becomes 'set' (both can mean to position or place something).
'a quadrangle' becomes 'square' (square is a kind of quadrangle).
'set'+'square'='SET-SQUARE'
'to' is the link.
Can you help me to learn more?
(Other definitions for set square that I've seen before include "Triangular shape for technical drawing" , "Right-angled plate for drawing lines" , "It helps drawing" , "Right-angled triangular drawing instrument" , "It may be used to help one draw" .)