D’Alembert already called the curve a ***lemniscate*** in the *Encyclopédie* (1765, vol. 9, [p. 382](https://archive.org/stream/encyclopdieoud09alem#page/382), [fig. 41](https://archive.org/stream/Recueildeplancht5Dide#page/n68)) which is probably where Gerono got his terminology. Cramer apparently called it a ***huit-de-chiffre*** ([1750](http://doi.org/10.3931/e-rara-4048), [p. 9](https://www.e-rara.ch/zut/content/pageview/1233359), [fig. 8H](https://www.e-rara.ch/zut/content/pageview/1233363)) or indeed ***besace*** ([p. 451](https://www.e-rara.ch/zut/content/pageview/1233819), [fig. 142](https://www.e-rara.ch/zut/content/pageview/1233839)), which translates as [*double sack*](http://www.systranet.com/translate) or [*wallet*](https://translate.google.com/#fr/en/besace) ([Oxford](https://archive.org/stream/newenglishdictio102murruoft#page/n412): “A bag having the opening in the middle, and a receptacle at each end. The wallet ‘with two pouches in it’ was prob. originally slung across the horse.”) The first two uses seem to go back to  [Bragelongne](https://fr.wikipedia.org/wiki/Christophe-Bernard_de_Bragelongne), in ([1732](https://archive.org/stream/histoiredelacad30laca#page/158), p. 164):

>Toutes les Courbes algébriques (...)
rentrent en elles-mêmes, ou s’étendent à l’infini.
Celles qui rentrent en elles-mêmes peuvent être appellées
*Ovales* (...) Ces *Ovales* sont ou simples comme l’Ellipse
ordinaire (...), ou composées (...) & parmi ces Ovales composées
il y en a qui se noüent en forme de ruban, & on les appelle
des ***Lemniscates***, nom qui leur a été imposé par les illustres
Géomètres de Bâle

and ([1733](https://archive.org/stream/histoiredelacad31laca#page/n58), p. 45):

>M. Bernoulli [[1694](https://www.e-rara.ch/zut/content/pageview/1040536)] a appelé *Lemniscate*, c’est-à-dire, *Ruban*, une Courbe qui ressemble à un **8 de chiffre**.

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**Update:**<br>
As found by C. Beenakker in the comments, the more general curve $(x^2-by)^2= a^2(x^2-y^2)$ was called ***parabola virtualis*** by Saint-Vincent ([1647](https://books.google.com/books?id=7e9VQAAACAAJ&pg=PA840), pp. 840-864); Teixeira ([1905](https://archive.org/stream/tratadodelascurv00gome#page/195), pp. 195-200) calls our case $b=0$ parabola virtualis ***recta***, and points after Loria ([1902](https://books.google.com/books?id=wp4LAAAAYAAJ&pg=PA172&dq=virtuelle+Parabel), pp. 172-179) to its discussion in Huygens-Sluse  correspondence ([1657](http://www.dbnl.org/tekst/huyg003oeuv02_01/), Nº 404, 406, 407, 414, 416, 424, 430).