Deficit stops firm investing at first huge figures (7)
I believe the answer is:
colossi
'huge figures' is the definition.
(I've seen this before)
'deficit stops firm investing at first' is the wordplay.
'deficit' becomes 'loss' (I've seen this in other clues).
'stops' means one lot of letters goes inside another (stopping can mean blocking a gap).
'firm' becomes 'co' (abbreviation for company).
'at first' says to take the initial letters.
The first letter of 'investing' is 'i'.
'co'+'i'='coi'
'loss' inserted inside 'coi' is 'COLOSSI'.
(Other definitions for colossi that I've seen before include "Powerful organisations" , "Powerful figures" , "huge figures" , "heavyweights" , "Cool sis for big people" .)