couplet

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A unit of verse consisting of two successive lines, usually rhyming and having the same meter and often forming a complete thought or syntactic unit.
2. n. Two similar things; a pair.

Century Dictionary and Cyclopedia

1. n. In prosody, two lines in immediate succession, usually but not necessarily of the same length, forming a pair, and generally marked as such by riming with each other. A pair of lines joined by rime is considered a couplet, whether it forms part of a stanza or constitutes a metrical group by itself. See distich.
2. n. In music, two equal notes inserted in the midst of triple rhythm to occupy the time of three; a temporary displacement of triple by duple rhythm.
3. n. One of a pair, as of twins; a twin.
4. n. In Gothic arch., a double window; one having two lights only and these of the same size and style.

Wiktionary

1. n. literature A pair of lines with rhyming end words.
2. n. A pair of one-way streets which carry opposing directions of traffic through gridded urban areas.

GNU Webster's 1913

1. n. Two taken together; a pair or couple; especially two lines of verse that rhyme with each other.

WordNet 3.0

1. n. a stanza consisting of two successive lines of verse; usually rhymed
2. n. two items of the same kind