__ Sulphate, Was Used as Rat Poison, Symbol Tl
Puzzle 8 of Astrology Medium Pack
Question is: __ Sulphate, Was Used as Rat Poison, Symbol Tl
and the answer is: THALLIUM
Word Meaning:
THALLIUM — A metallic chemical element (symbol Tl) with atomic number 81: a gray post-transition metal that discolors when exposed to air.
Definitions from Wiktionary.