[ kwə'tə:nɪən ]
■ noun
1》 Mathematics a complex number of the form w + xi + yj + zk , where w , x , y , z are real numbers and i , j , k are imaginary units that satisfy certain conditions.
2》 rare a set of four people or things.
Origin
C19: from late L. quaternio(n-) , from L. quarterni (see quaternary ).