Definitions
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. The infinity symbol (∞).
 n. Any closed curve (similar to a figure eight) described by a Cartesian equation of the form .
from The Century Dictionary and Cyclopedia
 In mathematics, related to the lemniscate of Bernoulli.
 In ichthyology, having a hyaline or transparent appearance and ribbonlike form; of or relating to the Lemniscati: as, a lemniscate fish.
 n. In mathematics:
 n. The locus of the point at which the tangent to an equilateral hyperbola meets the perpendicular let fall upon it from the center: a curve invented by James Bernoulli.
 n. Any crunodal curve of the fourth order having only one real branch, and this finite and symmetrical with respect to two axes.
 n. The locus of the point at which the tangent to a fixed conic is cut by a perpendicular let fall upon it from the center.
 n. A Cassinian: a misapplication of the word originating in Germany.
 n. The locus of the point in which the straight through the center and the projection of a point of a circle on a fixed tangent are cut by the perpendicular from this point to the diameter from the contact point.
Etymologies
from Wiktionary, Creative Commons Attribution/ShareAlike License
Examples

'lemniscate', a particular modification of the socalled Cassinian curves. 2 1

Her gaze was caught on the glowing wand and lemniscate, and she thought of radiation.

A lemniscate, an infinity symbol, glowed above his head.

You mentioned lemniscate periodic systems in one of your chemistry blogs.

The one Ariel did recognize shone bright white in the center of the robot's upper torso, a lemniscate crossed by an arrow at an upward angle: the sign of the Managins.

Some projectivegeometrical considerations concerning the lemniscate are to be found in the previously mentioned writings of G. Adams and L. L.cherErnst.

You have read, too, in _The Secret Doctrine, _ P.ofessor Crooke's theory, endorsed by H.P. Blavatsky, as to how the chemical elements were deposited by a spiral evolutive force, a creative impulse working outward in the form of a caduceus or lemniscate, or figure '8.'

About the epoch of maximum of sunspots they are large and nearly circular, having the same character as the curves for the summer months; whilst about the time of sunspot minimum they are small and lemniscateshaped, with a striking resemblance to the curves for the winter months.

According to the lemniscate arrangement, we should commence with hydrogen as the head of the first negative group, but as it differs wholly from those placed with it, it is better to take it by itself.
Occult Chemistry Clairvoyant Observations on the Chemical Elements

We follow here the grouping according to external forms, and the student should compare it with the groups marked in the lemniscate arrangement shown in Article II (p. 377, properly p. 437, February), reading the group by the disks that fall below each other; thus the first group is H, Cl, Br,
Occult Chemistry Clairvoyant Observations on the Chemical Elements
qms commented on the word lemniscate
Erect he's the humble number eight
But, privileged to help out the great,
And supple and nimble,
Reclines as a symbol,
So toppled becomes the lemniscate.
May 5, 2017
artoparts commented on the word lemniscate
See: limaçon (Heartlike shape for Valentines Day)
January 28, 2009
johnmperry commented on the word lemniscate
nor with Lissajou's figures.
August 26, 2008
sionnach commented on the word lemniscate
Not to be confused with a loxodrome
November 28, 2007
sarra commented on the word lemniscate
Describes a certain kind of figureofeight mathematical curve, an example of which is the infinity sign ∞.
The Latin root is lēmniscus, from the Greek λημνίσκος, lêmniskos, both referring to ribbons.
November 28, 2007