The Collaborative International Dictionary of English v.0.48:

Extravasate \Ex*trav"a*sate\, v. t. [imp. & p. p.
   Extravasated; p. pr. & vb. n. Extravasating.] [Pref.
   extra- + L. vas vessel: cf. F. extravaser. See Vase.]
   To force or let out of the proper vessels or arteries, as
   blood.
   [1913 Webster]