Then has 10 different meanings across 5 categories:
Noun · Adjective · Adverb · Conj · Proper Noun
That time
Being so at that time.
in 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"
At that time.
Obsolete spelling of than
A surname.
Then comes from Old English, originally meaning "at that time." It is related to the demonstrative word for "that" in ancient Indo-European languages.