By and by Meaning, Definition & Usage

  1. adverb at some eventual time in the future
    later.
    • By and by he'll understand
    • I'll see you later

WordNet

Definitions
  1. . (a) Close together (of place). Obs. "Two yonge knightes liggyng [lying] by and by." Chaucer. (b) Immediately; at once. Obs. "When . . . persecution ariseth because of the word, by and by he is offended." Matt. xiii. 21. (c) Presently; pretty soon; before long. In this phrase, by seems to be used in the sense of nearness in time, and to be repeated for the sake of emphasis, and thus to be equivalent to "soon, and soon," that is instantly; hence, less emphatically, pretty soon, presently.

Webster 1913