The Collaborative International Dictionary of English v.0.48:

Brimstone \Brim"stone\, n. [OE. brimston, bremston, bernston,
   brenston; cf. Icel. brennistein. See Burn, v. t., and
   Stone.]
   Sulphur; See Sulphur.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brimstone \Brim"stone\, a.
   Made of, or pertaining to, brimstone; as, brimstone matches.
   [1913 Webster]

         From his brimstone bed at break of day
         A-walking the devil has gone.            --Coleridge.
   [1913 Webster]

WordNet (r) 3.0 (2006):

brimstone
    n 1: an old name for sulfur [syn: brimstone, native sulfur,
         native sulphur]