This is the 51st most frequent German word.
nun
"Nun" means "now" or "well" (context-dependent).
'Nun' is used here as an adverb indicating the current point in time.
Nun ist es an der Zeit zu gehen.
Now it is time to leave.
'Nun' is used here to begin a statement, functioning as a conversational interjection similar to 'well' in English.
Nun, das erklärt einiges.
Well, that explains a lot.
'Nun' is again used as an adverb to indicate a moment in time, specifically the present moment.