1. adverb /ðɛn,ðen/
a) at that time
He was happy then.
b) soon afterward.
He fixed it, then left.
2. adjective /ðɛn,ðen/
being so at that time
3. noun /ðɛn,ðen/
that time<!is this pronoun?
It will be finished before then.
Wikipedia foundation.