Left one million? It is the maximum amount (5)
I believe the answer is:
limit
'the maximum amount' is the definition.
'limit' can be an answer for 'amount' (limit is a kind of amount). I am not certain of the 'the maximum' bit.
'left one million? it' is the wordplay.
'left' becomes 'l' (common abbreviation).
'one million?' becomes 'im' (resembles 1m).
'l'+'im'+'it'='LIMIT'
'is' is the link.
Can you help me to learn more?
(Other definitions for limit that I've seen before include "As far as something can go" , "Restrict to a specified amount" , "qualify?" , "Boundary, demarcation line" , "end" .)