Afterward means at a later time than the thing described. Shortly afterward, long afterward, afterward they went home.
This is the American form; British English writes afterwards with an s, and both are correct in their own places. It refers back to something already mentioned, which is why it cannot start a narrative. Note that afterword with an o is a different thing entirely — the piece at the end of a book; and that the -ward and -wards pair works the same way in toward, forward and backward.
1adverbafterwardAt a later time than the thing described.
“We went to the cinema and had dinner afterward.”
afterward is a reference to later time.
Old English aefterweard is after plus -weard, meaning turned towards — the same ending as in toward and homeward. The s of afterwards was an old genitive that American English dropped and British kept.
Old English
æfterweard
Middle English
afterward
English, today
afterward
Middle English afterward, from Old English æfterweard; equivalent to after + ward.
Etymology from Wiktionary, CC BY-SA