From Middle English by and by, equivalent to by + and + by.

by and by (not comparable)

1. After a short time.
   • a. 1822, Percy Bysshe Shelley "On the Symposium, or Preface to the Banquet of Plato"

     "You are laughing at me, Socrates," said Agathon, "but you and I will decide this controversy about wisdom by and by, taking Bacchus for our judge. At present turn to your supper."

2. After an indefinite period.

   Sit down, have a rest, and by and by you'll be feeling better.

3. (obsolete) Immediately; at once.
   • 1611, The Holy Bible, […] (King James Version), London: […] Robert Barker, […], →OCLC ↗, Matthew 13:21 ↗:

     When […] persecution ariseth because of the word, by and by he is offended.

• (after a short time) shortly, soon; see also Thesaurus:soon
• (after an indefinite period) in due course, sooner or later; see also Thesaurus:eventually
• (immediately) now, stat; see also Thesaurus:immediately

• Russian: со временем

by and by (uncountable)

1. Heaven; the hereafter. Usually preceded with "the sweet."

   I'm sorry ma'am, but your cat's gone on to the sweet by and by.

• other side, spirit world, sweet hereafter: see also Thesaurus:afterlife

• Russian: мир ино́й