Snake in square pot (4)
I believe the answer is:
turn
'snake' is the definition.
(thesaurus)
'square pot' is the wordplay.
'square' becomes 't' (a T-Square is a technical drawing instrument).
'pot' becomes 'urn' (urn is a kind of pot).
't'+'urn'='TURN'
'in' acts as a link.
(Other definitions for turn that I've seen before include "rotation" , "Shape (using a lathe)" , "fit" , "Rotate - go" , "Move around an axis, or change" .)