i·mag·i·nar·y 
(ĭ-măjə-nĕr′ē)
(ĭ-măjə-nĕr′ē)adj.
1. Having existence only in the imagination; unreal.
2. Mathematics
a. Of or being the coefficient of the imaginary unit in a complex number.
b. Of, involving, or being an imaginary number.
c. Involving only a complex number of which the real part is zero.
n. pl. i·mag·i·nar·ies
Mathematics
Mathematics
An imaginary number.
i·mag′i·nari·ly adv.
i·mag′i·nari·ness n.