brimstone

Boyd’s Bible Dictionary:

(burn-stone). Sulfur (Gen. 19:24), of frequent figurative use (Job 18:15; Psa. 11:6; Isa. 34:9; Rev. 21:8).

Concise Bible Dictionary:

Bitumen, pitch, or sulfur, which is still found in its crude state in Palestine. In God’s judgment it was rained from heaven (Gen. 19:24; Psa. 11:6; Ezek. 38:22; Luke 17:29). It is symbolical of that which will add to the torment and anguish of the wicked (Rev. 14:10; Rev. 19:20; Rev. 20:10; Rev. 21:8).

Strong’s Dictionary of Greek Words:

Greek:
θεῖον
Transliteration:
theion
Phonic:
thi’-on
Meaning:
probably neuter of 2304 (in its original sense of flashing); sulphur
KJV Usage:
brimstone