Definition of "Then" :

noun: that time; that moment

"We will arrive before then."

adjective: at a specific prior time

"The then president."

adverb: subsequently or soon afterward (often used as sentence connectors)

"Then he left."

adverb: at that time

"I was young then."

adverb: in that case or as a consequence

"If he didn't take it, then who did?."