Triangular item assigned shape (3,6)
I believe the answer is:
set square
'triangular item' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe you can see an association between them that I don't see?
'assigned shape' is the wordplay.
'assigned' becomes 'set' (I've seen this in another clue).
'shape' becomes 'square' (squaring is a kind of shaping).
'set'+'square'='SET-SQUARE'
Can you help me to learn more?
(Other definitions for set square that I've seen before include "design tool (that's right)" , "Right-angled triangular drawing instrument" , "Right-angled plate for drawing lines" , "It may be used to help one draw" , "Triangular shape for technical drawing" .)