(3 syl.) means the “sailing stars” (Greek, pleo, to sail), because the Greeks considered navigation safe at the return of the Pleiades, and never attempted it after those stars disappeared.
The PLEIADES were the seven daughters of Atlas and Pleione. They were transformed into stars, one of which (Merope) is invisible out of shame, because she alone married a human being. Some call the invisible star “Electra,” and say she hides herself from grief for the destruction of the city and royal race of Troy.
i. The Pleiad of Alexandria. A group of seven contemporary poets in the reign of Ptolemy Philadelphos; so called in reference to the cluster of stars in the back of Taurus. Their names are- Callimachos, Apollonios of Rhodes, Aratos, Philiscos (called Homer the Younger), Lycophron, Nicander, and Theocritos.
There are in reality eleven stars in the Pleiades. ii. The literary Pleiad of Charlemagne. Alcuin (Albinus), Angilbert (Homer), Adelard (Augustine), Riculfe (Damaetas), Charlemagne (David), Varnefrid, and Eginhard.
iii. The first French Pleiad. Seven contemporary poets in the sixteenth century, in the reign of Henri III., who wrote French poetry in the metres, style, and verbiage of the ancient Greek and Latin poetry. Of these, Ronsard was by far the most talented; but much that would be otherwise excellent is spoilt by pedantry and Frenchified Latin. The seven names are Ronsard, Dorat, Du Bellay, Remi-Belleau, Jodelle, Baïf, and Thiard.
Letitia Elizabeth Landon published, in 1829, a poem entitled The Lost Pleiad. (See above, Pleiades.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894