This is the 17976th most frequent Polish word.
śmiertelna
"Śmiertelna" means "fatal" or "deadly" in English.
Here, 'śmiertelna' is used as an adjective to describe 'poison', conveying its capacity to cause death.
To była śmiertelna trucizna.
It was a deadly poison.
In this example, 'śmiertelnych' is the plural form used as an adjective to describe 'dangers', emphasizing their lethal nature.
Ludzie powinni unikać śmiertelnych zagrożeń.
People should avoid deadly dangers.
Here 'śmiertelna' metaphorically describes the 'silence', likening its intensity to a state associated with death.