black work

US: (blak′wûrk′)

WordReference Random House Unabridged Dictionary of American English © 2025

black′ work′, 

1. work for which a person is paid in cash, with the transaction not recorded or reported, so as to avoid paying income tax on the amount earned.
2. Clothing blackwork.

black•work  (blak′wûrk′), n. 

1. Clothing embroidery done with black, usually silk, thread on white fabric, esp. linen.

Also, black work. 

• black + work