This is the 7797th most frequent Dutch word.
dodelijk
Deadly.
Here, 'dodelijk' descriptively emphasizes the intensity or extremity of how 'stil' (quiet) the situation turned.
De situatie werd ineens dodelijk stil.
The situation suddenly became deadly quiet.
Here, 'dodelijk' is used as an adjective describing 'vergif', indicating it has the potential to cause death.
Het vergif dat hij gebruikte was dodelijk.
The poison he used was lethal.
In this example, 'dodelijk' functions to intensify the description of 'saaie', using hyperbole to emphasize how boring the jokes are.