Questions & Answers about Birden yağmur başladı.
Birden literally comes from bir (one) + -den (from), but as a whole it’s an adverb meaning roughly:
- all of a sudden
- suddenly
- out of nowhere / out of the blue
So Birden yağmur başladı ≈ Suddenly, (the) rain started or All of a sudden, it started to rain.
Nuances with similar words:
- birden – very common, neutral, everyday
- birdenbire – a bit stronger, like all of a sudden (slightly more emphatic)
- aniden – more formal/literary, like suddenly / abruptly
All three can work here:
- Birden yağmur başladı.
- Birdenbire yağmur başladı.
- Aniden yağmur başladı.
The meaning is basically the same, just tiny differences in feel and register.