رباعي

Etymology
, from the root ; related to the numeral.

Adjective

 * 1) consisting of four, quadripartite, fourfold, quadruple
 * 2)  quadrangular
 * 3)  tetragonal
 * 4)  consisting of four radical letters, quadriliteral

Noun

 * 1)  relay team of four
 * 2)  quartet
 * 3)  quatrain

Usage notes
The meaning “quatrain” uses the plural.