Synonyms for In the old days:

• a. & adv.

  •once (adjective, adverb)
  • more before.
  •Other relevant words: (adjective, adverb)
  • time was,
  • Whilom,
  • once only,
  • in times gone by,
  • this time.

• adv.

  •once (adverb)
  • before,
  • already,
  • heretofore,
  • earlier,
  • previously,
  • late,
  • back,
  • sometime,
  • erstwhile,
  • one,
  • old,
  • bygone,
  • away back,
  • quondam.

• adv

  •Other relevant words: (adverb)
  • at one time,
  • in old days,
  • in olden days,
  • only one time,
  • one time previously,
  • back when,
  • but once,
  • on one occasion,
  • in the olden days,
  • long ago,
  • a single time,
  • on occasion,
  • in times past,
  • one time before,
  • once upon a time,
  • once.

• Other synonyms:

  •
  • atavistic,
  • formerly.
  •
  • removed.

Antonyms for In the old days:

• adv.

  • once
    later, future, presently, currently.