Pete blunders, stupidly purchasing small undergarment (9-4)
I believe the answer is:
suspender belt
'undergarment' is the definition.
(I've seen this before)
'pete blunders stupidly purchasing small' is the wordplay.
'stupidly' indicates an anagram (a stupid ordering of the letters).
'purchasing' means one lot of letters goes inside another (some letters take possession of others).
'small' becomes 's' (abbreviation - e.g. clothes size).
'pete'+'blunders'='peteblunders'
'peteblunders' with letters rearranged gives 'supenderbelt'.
'supenderbelt' placed around 's' is 'SUSPENDER-BELT'.
(Other definitions for suspender belt that I've seen before include "Undergarment" , "underwear" , "Item for holding up a woman's stockings" .)