From WordNet (r) 3.0 (2006) [wn]:
afterwards
adv 1: happening at a time subsequent to a reference time; "he
apologized subsequently"; "he's going to the store but
he'll be back here later"; "it didn't happen until
afterward"; "two hours after that" [syn: subsequently,
later, afterwards, afterward, after, later on]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Afterwards \Aft"er*wards\, Afterward \Aft"er*ward\, adv. [AS.
[ae]fteweard, a., behind. See Aft, and -ward (suffix).
The final s in afterwards is adverbial, orig. a genitive
ending.]
At a later or succeeding time.
[1913 Webster]