Lexical Definition

‎ὕαλος‎ hýalos (hoo'-al-os) glass ^G:N-M
perhaps from the same as ‎ὑετός‎ (as being transparent like rain)

glass.

Abbott-Smith

ὕαλος, -ου, ὁ [in LXX: Jb 28:17 (זְכוּכִית) * ;]
1. (Hdt.) a clear transparent stone.
2. (from Plat. on) glass: Re 21:18, 21.†

Abbott-Smith References

Liddell-Scott-Jones

ὕαλος

or ὕελος (see. below), ἡ, see [Refs 4th c.BC+], ὁ:—the form ὕαλος is said to be Attic dialect, ὕελος Hellenic, [Refs 5th c.BC+] and ὕαλο; ὕελος is read in [NT+4th c.BC+]; compare ὑάλινος:—originally some kind of crystalline stone, such as that used by the Ethiopians to enclose their mummies in, [Refs 5th c.BC+]rock-crystal, [Refs 3rd c.AD+]

__2 a convex lens of crystal, used as a burning-glass, λίθος διαφανὴς ἀφ᾽ ἧς τὸ πῦρ ἅπτουσι [Refs 5th c.BC+]
__II glass, first in [Refs 5th c.BC+]glass-ware, [Refs 4th c.AD+]
__III ὕαλος χνοώδης, in [Refs 7th c.AD+], is an absorbent of some kind:—ὕαλος is also explained by βόρβορος in [Refs 5th c.AD+]. [ῠᾰλος, as appears from [Refs 5th c.BC+]:—but late Poets make ῡ in some derivations to bring them into dactylic verses, ῡάλεος [Refs]; ῡέλινος [Refs]; ῡαλόεις [Refs]; ῡαλοειδής [Refs 5th c.AD+]; in iambic metre, ῡαλόχροα [Refs]

_{LSJ Scripture Refs: LXX.Job.28.17 ☩ Rev.21.18}