5 of the books of Kesuvim are called Megillas (Maseches Sofrim 14:3 identifies 4 of them, Rus, Shir Hashirim, Eicha, and Ester. Rishonim cite versions that add in Koheles - e.g. Mordechai Megilla ...
Many a Jewish book is known colloquially by its title, like Avne Nezer and More N'vuchim. Many a one is known colloquially by its author's name, like the commentaries of R' Moshe Alshich and Malbim on ...