When you apply undue pressure about minor measures, it means business (8)
I believe the answer is:
commerce
'business' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for commerce that I've seen before include "Transactions in goods and services" , "Trading exchanges" , "Business, industry, trade" , "Trading activity" , "Traffic" .)