Origin: 1250–1300; Middle English dite < Anglo-French, Old French dit(i)e poem, noun use of past participle of ditier to compose < Latin dictāre;see dictate
c.1300, from O.Fr. ditie "composition, poem, treatise," from L. dictatum "thing dictated," neut. pp. of dictare "dictate." Ditty bag is 1850s nautical slang, perhaps from Brit. naval phrase commodity bag.