Word Study
thio-
CIDE DICTIONARY
thio-, [Gr. brimstone, sulphur.].
A combining form (also used adjectively) denoting the presence of sulphur. See Sulpho-. [1913 Webster]
OXFORD DICTIONARY
thio-, comb. form sulphur, esp. replacing oxygen in compounds (thio-acid).
Etymology
Gk theion sulphur
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