The Collaborative International Dictionary of English v.0.48:

circumstant \cir"cum*stant\ (s[~e]r"k[u^]m*st[a^]nt), a. [L.
   circumstans. See Circumstance.]
   Standing or placed around; surrounding. [R.] "Circumstant
   bodies." --Sir K. Digby.
   [1913 Webster]