once upon a time

once upon a time

A long time ago in the past. Used predominantly as a clichéd opening to fairy tales or stories for young children. Once upon a time, there lived a princess who was training to be a fearsome warrior. Even I was young once upon a time, if you can believe that.
See also: once, time, upon
Farlex Dictionary of Idioms.

once upon a time

Cliché once in the past. (A formula used to begin a fairy tale.) Once upon a time, there were three bears. Once upon a time, I had a puppy of my own.
See also: once, time, upon
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

once upon a time

On some past occasion, as in I may have sung this piece once upon a time, but I don't really remember it. This phrase, first recorded in 1595, is frequently used as the opening line of fairy tales and stories told to children, as in Once upon a time there was a king who had three beautiful daughters.
See also: once, time, upon
The American Heritage® Dictionary of Idioms by Christine Ammer.

once upon a time

1 at some time in the past (used as a conventional opening of a story). 2 formerly.
See also: once, time, upon
Farlex Partner Idioms Dictionary

ˌonce upon a ˈtime

used, especially at the beginning of children’s stories, to mean ‘a long time in the past’: Once upon a time in a faraway land there lived a princess in a big castle.
See also: once, time, upon
Farlex Partner Idioms Dictionary
See also:
  • (it's) (a)bout time
  • about time
  • about time too
  • a year and a day
  • any time
  • anytime
  • a week from next Tuesday
  • any time means no time
  • any old time
  • (it's) time to go
References in periodicals archive
Colin O'Donoghue: 'Once Upon A Time' Actor Teases Captain Hook's Story Arc In Second Half Of Season 4 - [(http://au.ibtimes.com/articles/576318/20141217/colin-o-donoghue-once-upon-time-actor.htm#.VJg8-cEPk) READ ]