Nouns

(n)thenthat time; that moment“we will arrive before then”, “we were friends from then on”

Adjectives

(s)thenat a specific prior time“the then president”

Adverbs

(r)then, so, and sosubsequently or soon afterward (often used as sentence connectors)“then he left”, “go left first, then right”, “first came lightning, then thunder”, “we watched the late movie and then went to bed”, “and so home and to bed”
(r)thenin that case or as a consequence“if he didn't take it, then who did?”, “keep it then if you want to”, “the case, then, is closed”, “you've made up your mind then?”, “then you'll be rich”
(r)thenat that time“I was young then”, “prices were lower back then”, “science as it was then taught”