Very small number — very little, minus one million (7)
I believe the answer is:
nominal
'very small' is the definition.
(as in a nominal fee)
'number very little minus one million' is the wordplay.
'number' becomes 'no.' (abbreviation for 'number').
'very little' becomes 'minimal' (I've seen this before).
'minus' suggests deleting specific letters.
'one million' becomes 'im' (resembles 1m, 1 million).
'minimal' with 'im' taken away is 'minal'.
'no'+'minal'='NOMINAL'
(Other definitions for nominal that I've seen before include "Titular" , "Token - lion man (anag)" , "unreal" , "In name or form only" , "trifling" .)