month of Sundays

month of Sundays  {n. phr.},  {informal}
A very long time. — Used for emphasis after "for" or "in" and usually with a negative verb.
I have not had devil's food cake in a month of Sundays.
When he got her first letter, he felt that he had not heard from her for a month of Sundays.
Syn.: DOG'S AGE.
Categories: emphasis time {informal} {n. phr.}