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?."