conjunction
because, since
A1
Da is a subordinating conjunction meaning because or since, used to introduce a subordinate clause and express reason. It sends the conjugated verb to the end of the clause (verb-final order). Common at the start of sentences; slightly more formal or literary than weil in many contexts.
Examples
Da es stark regnete, blieben wir zu Hause.
Because it rained heavily, we stayed at home.
Da er krank war, konnte er nicht kommen.
Since he was ill, he couldn't come.
Da der Vertrag zu spät unterschrieben wurde, kündigte die Firma das Angebot.
Since the contract was signed too late, the company canceled the offer.
Details
Mnemonics
Imagine a reason arrow pointing from cause to effect when you say 'da' (because).
Pronounce like English 'da' — short and causal.
Notes
'Da' as a subordinating conjunction introduces a reason and behaves like 'weil' but is slightly more formal/neutral.