Erect in the centre and mess with quadrilateral (9)
I believe the answer is:
rectangle
'quadrilateral' is the definition.
(I know that rectangle is a type of parallelogram)
'erect in the centre and mess' is the wordplay.
'in the centre' indicates the central letters.
'and' means one lot of letters go next to another.
'mess' becomes 'tangle' (I've seen this before).
The middle of 'erect' is 'rec'.
'rec'+'tangle'='RECTANGLE'
'with' is the link.
(Other definitions for rectangle that I've seen before include "Quadrilateral" , "Four sides involved in this" , "box" , "Geometric figure with four right angles, not square" , "Parallelogram with four right angles" .)