What is "deraign"

Deraign \De*raign"\, Derain \De*rain"\, v. t. [See Darraign.] (Old Law) To prove or to refute by proof; to clear (one's self). [Obs.]

vb. 1 (context legal obsolete transitive English) To prove or to refute by proof, especially on threat of combat. 2 (context obsolete English) To engage in (battle, combat etc.).