This is the 4718th most frequent Polish word.
nielegalnego
"Nielegalnego" means "illegal."
The word 'nielegalnego' in this sentence is used as an adjective in the genitive case to describe 'trade', indicating unlawful commerce.
Odkryliśmy ślad nielegalnego handlu.
We discovered traces of illegal trade.
Here, 'nielegalnego' modifies 'materialu', specifying the type in the genitive case and indicating prohibition.
Nielegalnego materiału nie można tutaj używać.
Illegal material cannot be used here.
In this context, 'nielegalnego' functions as an adjective in the genitive case describing 'act', emphasizing the unlawful nature of the action.