Quadrilateral pit made with a dozer (9)
I believe the answer is:
trapezoid
'quadrilateral' is the definition.
(I know that trapezoid is a type of quadrilateral)
'pit made with a dozer' is the wordplay.
'made with' is an anagram indicator.
'a'+'dozer'='adozer'
'pit' mixed up with 'adozer' makes 'TRAPEZOID'.
(Other definitions for trapezoid that I've seen before include "Type of quadrilateral" , "Prize toad (anag.)" , "Form of quadrilateral" , "Figure" .)