Real Dictionary

limerick
countable noun: A limerick is a humorous poem which has five lines.

Limerick in American English
a nonsense poem of five anapestic lines, now often bawdy, usually with the rhyme scheme aabba, the first, second, and fifth lines having three stresses, the third and fourth having two: the form was popularized by Edward Lear (Ex.: There was a young lady
county in SW Ireland, in Munster province: 1,037 sq mi (2,686 sq km); pop. 110,000
noun: a fishhook having a sharp bend below the barb
noun: a kind of humorous verse of five lines, in which the first, second, and fifth lines rhyme with each other, and the third and fourth lines, which are shorter, form a rhymed couplet

limerick in British English
noun: a county of SW Republic of Ireland, in N Munster province: consists chiefly of an undulating plain with rich pasture and mountains in the south. County town: Limerick. Pop: 175 304 (2002). Area: 2686 sq km (1037 sq miles)
noun: a form of comic verse consisting of five anapaestic lines of which the first, second, and fifth have three metrical feet and rhyme together and the third and fourth have two metrical feet and rhyme together