lemniscate
noun
lem·nis·cate lem-ˈni-skət 
: a figure-eight shaped curve whose equation in polar coordinates is ρ2=a2 cos 2θ or ρ2=a2 sin 2θ
Word History
Etymology
New Latin lemniscata, from feminine of Latin lemniscatus with hanging ribbons, from lemniscus
First Known Use
circa 1781, in the meaning defined above