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. Synonym: DOG'S AGE.
[TahlilGaran] English Idioms Dictionary ▲