This is the 73rd most frequent Icelandic word.
síðan
"Since" or "then."
The word 'síðan' here functions as an adverb meaning 'ago', used to indicate a point in the past.
Ég sá hana fyrir löngu síðan.
I saw her a long time ago.
In this sentence, 'síðan' acts as a conjunction equivalent to 'then', showing a sequential action.
Hann borðaði og síðan fór hann í göngu.
He ate and then he went for a walk.
Here, 'síðan' is a preposition meaning 'since', indicating a time period starting from a previous point up to now.