1. in a short time; soon.
2. at another time.
3. Archaic. at once; immediately.
And anon when his breathing had become deep and regular, we may creep into his bedroom and catch him at his dreams.
— H. G. Wells , The Wheels of Chance , 1896
He waved good-bye and told me he’d call anon. That time, I didn’t fall for the anon thing.
— Patricia A. Marx , Him Her Him Again the End of Him , 2007
Anon comes from the Old English phrase on āne meaning “in one (course)” or “straightaway.”