Strong's G5194 · Greek

ὕαλος

hualos · hoo'-al-os

perhaps from the same as 5205 (as being transparent like rain); glass

Scholarly Lexicons

Abbott-Smith Manual Greek Lexicon

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

G. Abbott-Smith, A Manual Greek Lexicon of the New Testament (1922) — public domain