Thousands spent by top clubs? (4)
I believe the answer is:
suit
'clubs?' is the definition.
(clubs is an example of a card suit)
'thousands spent by top' is the wordplay.
'thousands' becomes 'mm' (Roman numerals).
'spent by' is a deletion indicator.
'top' becomes 'summit' ('summit' can be a synonym of 'top').
'summit' with 'mm' taken out is 'SUIT'.
(Other definitions for suit that I've seen before include "See 1" , "Eg, spades" , "It constitutes one quarter of a deck" , "Legal action - courtship" , "clubs, for example" .)