The Collaborative International Dictionary of English v.0.48:

Circumstantiate \Cir`cum*stan"ti*ate\, v. t. [imp. & p. p.
   Circumstantiated; p. pr. & vb. n. Circumstantiating.]
   [See Circumstantiating (?).]
   [1913 Webster]
   1. To place in particular circumstances; to invest with
      particular accidents or adjuncts. [R.]
      [1913 Webster]

            If the act were otherwise circumstantiated, it might
            will that freely which now it wills reluctantly.
                                                  --Bramhall.
      [1913 Webster]

   2. To prove or confirm by circumstances; to enter into
      details concerning.
      [1913 Webster]

            Neither will time permint to circumstantiate these
            particulars, which I have only touched in the
            general.                              --State Trials
                                                  (1661).
      [1913 Webster]