underground economy 
noun
North American term for black economy.Thus, it may be that the most widely accepted estimates of the size of the underground economy in advanced market capitalist economies rely upon estimates of the use of currency compared to GDP....
- A black market is also called an underground economy or unregulated economy.
- He defines ‘legal GDP’ as officially reported GDP minus the underground economy's GOP.
- notate
- not a thing
- not at home
- notatin
- notation
- notational
- notationally
- notationist
- notative
- notator
- not bat (or without batting) an eyelid (or eye or eyelash)
- not be able to do something a lick
- not be able to do something for toffee
- not be above
- not be an option
- not bear thinking about
- not before time
- not be fussy
- not-being
- (not) be myself
- not be oneself
- (not) be ourselves
- not be someone's first rodeo (or not be someone's first time at the rodeo)
- not best pleased
- (not) be themselves