other
since then, ever since
B1
Seitdem means “since then” or “ever since.” It’s a temporal adverb or subordinating conjunction: it can introduce a subordinate clause (verb-final) or function adverbially. Use it to link a past reference point to a continuing situation. Not reflexive or auxiliary; no case governance or irregular morphology.
Examples
Er hat viel gearbeitet; seitdem ist er ruhiger.
He worked a lot; ever since, he's been quieter.
Seitdem die Bibliothek geschlossen wurde, kamen weniger Studierende, sodass viele Plätze leer blieben.
Since the library was closed, fewer students came, so many seats remained empty.
Seitdem regnet es öfter.
Since then, it has been raining more often.
Details
Mnemonics
a clock with an arrow pointing from a past moment to the present
sounds like 'sight them' — imagine remembering a sight since that time
Notes
Used as a temporal conjunction or adverb meaning 'since that time'. Common in both spoken and written German.