month of Sundays, a

a month of Sundays

An extremely long, often indefinite period of time. Often used in negative constructions, especially to mean "never." A: "Do you think Samantha will agree to go on a date with Jake?" B: "Not in a month of Sundays!" We'll be here for a month of Sundays trying to sort through all this paperwork!
See also: month, of, Sundays
Farlex Dictionary of Idioms.

month of Sundays, a

A long time, as in I haven't seen Barbara in a month of Sundays. This expression, which would literally mean thirty weeks, has been used hyperbolically since it was first recorded in 1832. One writer suggests it originally connoted a long dreary time, since games and other kinds of amusement used to be forbidden on Sunday.
See also: month, of
The American Heritage® Dictionary of Idioms by Christine Ammer.

a month of Sundays

a very long, seemingly endless period of time.
This expression may be a reference to the traditionally slow passage of Sundays as a result of religious restrictions on activity or entertainment. In a letter written in 1849 , G. E. Jewsbury talked of the absence of mail deliveries on Sundays, remarking: ‘If I don't get a better letter from you…you may pass “a month of Sundays” at breakfast without any letter from me’.
1998 Country Life All in all, the Ministry of Agriculture is gaining the no-nonsense, get-your-coats-off atmosphere that Jack Cunningham could not have managed in a month of Sundays.
See also: month, of, Sundays
Farlex Partner Idioms Dictionary

(not for/in) a ˌmonth of ˈSundays

(spoken) used to emphasize that something will never happen: ‘Do you think she’ll be able to sell the house at that price?’ ‘Not in a month of Sundays. It’s far too much.’
See also: month, of, Sundays
Farlex Partner Idioms Dictionary

month of Sundays

Informal
An indefinitely long period of time: It will take you a month of Sundays to chop all that wood.
See also: month, of, Sundays
American Heritage® Dictionary of the English Language, Fifth Edition.

month of Sundays, a

A very long time. It is doubtful that this expression, which dates from the early nineteenth century, was ever meant literally—that is, a period of thirty Sundays (or weeks). It first appeared in print in Frederick Marryat’s Newton Forster (1832) and was surely a cliché by the time Ogden Nash played on it in “My Dear, How Did You Ever Think up This Delicious Salad?” (1935): “The salad course nowadays seems to be a month of sundaes.” The British version, a week of Sundays, is never heard in America.
See also: month, of
The Dictionary of Clichés by Christine Ammer
See also:
  • a month of Sundays
  • month
  • month of Sundays
  • Sundays
  • breathe
  • breathe (something) to (someone)
  • do (something) to death
  • do something to death
  • cough it up
  • Cough it up!