ditty (n.)

"short song or poem intended to be sung to a simple melody,"early 14c., from Old French ditie "composition, poem, treatise," from Latin dictatum "thing dictated," neuter past participle of dictare "dictate," frequentative of dicere "to say, speak" (from PIE root *deik- "to show," also "pronounce solemnly"). In Middle English used of any literary composition, including dramas, essays, letters.