The Collaborative International Dictionary of English v.0.48:

Thenceforth \Thence`forth"\, adv.
   From that time; thereafter.
   [1913 Webster]

         If the salt have lost his savor, wherewith shall it be
         salted? it is thenceforth good for nothing. --Matt. v.
                                                  13.
   [1913 Webster]

   Note: This word is sometimes preceded by from, -- a
         redundancy sanctioned by custom. --Chaucer. --John.
         xix. 12.
         [1913 Webster]

WordNet (r) 3.0 (2006):

thenceforth
    adv 1: from that time on; "thereafter he never called again"
           [syn: thereafter, thenceforth]