a book of the Hebrew scriptures (the Song of Solomon, Ruth, Lamentations, Ecclesiastes, and Esther) appointed to be read on certain Jewish notable days, especially the Book of Esther, read at the festival of Purim.
(as noun the whole megillah) North American informal something in its entirety, especially a complicated set of arrangements or a long-winded story:you usually get the whole megillah, complete to the last screw
from Hebrew mĕḡillāh, literally 'scroll'
Megillah in other Oxford dictionaries
Definition of Megillah in the US English dictionary