The headword is mentioned only in lexica and grammars, usually (as here) in the nominative plural, though ps.-Zonaras has the singular. According to Hesychius (beta451), these were used as crowns for victors at Sparta. LSJ entry at web address 1.
Chantraine says that grammarians disputed whether this word should be spelled with ei or i, but the etymology is unknown. Frisk summarizes the proposed etymologies.