This is the 4437th most frequent Turkish word.
aniden
Suddenly.
Here, 'aniden' is used to indicate that the action of the door opening happened abruptly and without prior indication.
Aniden kapı açıldı.
Suddenly, the door opened.
In this sentence, 'aniden' is used to describe the unexpected commencement of the bird's flight.
Kuş aniden uçmaya başladı.
The bird suddenly started to fly.
Here, 'aniden' emphasizes the surprising and abrupt nature of the rain starting to fall.