Webster's Revised Unabridged Dictionary · 1913

Limerick

Limerick (lim"ẽr*ik) , noun

[Said to be from a song with the same verse construction, current in Ireland, the refrain of which contains the place name Limerick.]

It often begins with "There once was a..." or "There was a..."; as --

A humorous, often nonsensical, and sometimes risqé poem of five anapestic lines, of which lines 1, 2, and 5 are of three feet, and rhyme, and lines 3 and 4 are of two feet, and rhyme.
There was a young lady, Amanda, Whose Ballades Lyriques were quite fin de Siècle, I deem But her Journal Intime Was what sent her papa to Uganda.