Lexical Definition

‎שְׁבוּ‎ shᵉbûw (sheb-oo') agate ^H:N-F
from an unused root (probably identical with that of ‎שָׁבָה‎ through the idea of subdivision into flashes or streamers (compare ‎שָׁבִיב‎) meaning to flame

agate.

• a gem (from its sparkle), probably the agate

1) a precious stone (in the high priest's breastplate)
1a) probably an agate

Brown-Driver-Briggs

‎שְׁבוֺ‎ noun [feminine] a precious stone (relation to above √ dubious; = Assyrian šubû ᵐ5 ᵑ9 agate); — Exod 28:19=Exod 39:12 (+‎לֶשֶׁם‎, ‎אַחְלָ֑מָה‎).

Brown-Driver-Briggs References