The Collaborative International Dictionary of English v.0.48:

Quatrain \Quat"rain\, n. [F., fr. quatre four, L. quattuor,
   quatuor. See Four.] (Pros.)
   A stanza of four lines rhyming alternately. --Dryden.
   [1913 Webster]

WordNet (r) 3.0 (2006):

quatrain
    n 1: a stanza of four lines

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "quatrain":
   Spenserian stanza, antistrophe, book, burden, canto, chorus,
   couplet, distich, envoi, epode, heptastich, hexastich, line,
   measure, monostich, octastich, octave, octet, ottava rima,
   pentastich, refrain, rhyme royal, septet, sestet, sextet, stanza,
   stave, strain, strophe, syllable, tercet, terza rima, tetrastich,
   triplet, tristich, verse