Exact historical dictionary sense
Then in Webster's 1913 dictionary
The 1913 record labels then as adverb. Its source-bounded etymology and selected historical definition appear below.
[Originally the same word as than. See Than.]
Cross-verified historical senseIn Webster's Revised Unabridged Dictionary (1913), "then" is labeled adverb. Its etymology is recorded as: "[Originally the same word as than. See Than.]" The selected historical definition says: "At that time (referring to a time specified, either past or future)."