This is the 1558th most frequent German word.
gefährlichen
Dangerous.
The word "gefährlichen" describes the storm as dangerous, functioning here as an adjective in the genitive case to modify "Gewitter".
Das gefährlichen Gewitter zwang uns, drinnen zu bleiben.
The dangerous storm forced us to stay inside.
The word "gefährlichen" modifies "Abenteuer" in the accusative case to indicate the adventurous experiences as dangerous.
Er erzählt eine Geschichte über gefährlichen Abenteuer.
He tells a story about dangerous adventures.
Here, "gefährlichen" describes "Tiere" as dangerous animals, with the adjective in the nominative plural form due to its agreement with the subject.