Strong’s Greek
G2306 — theiodes
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
θειώδης
theiodes — pronounced thi-o'-dace
from 2303 and 1491; sulphur-like, i.e. sulphurous:--brimstone. see GREEK for 2303
1 occurrence in the KJV.
Revelation 9:17
And thus I saw the horses in the vision, and them that sat on them, having breastplates of fire, and of jacinth, and brimstone: and the heads of the horses were as the heads of lions; and out of their mouths issued fire and smoke and brimstone.