The story
From eft (“again, after”) + soon + -s (“adverb suffix”) – both senses (“soon after”, “again”) derive from senses of eft, which is related to after. Compare modern English soon after.
First known use, by meaning
- 11th–17th c. Once again; another time.
- from 13th c. Soon after, presently.
Etymology from Wiktionary, CC BY-SA 4.0.