The Collaborative International Dictionary of English v.0.48:

Implead \Im*plead"\, v. t. [imp. & p. p. Impleaded; p. pr. &
   vb. n. Impleading.] [Cf. Emplead.] (Law)
   To institute and prosecute a suit against, in court; to sue
   or prosecute at law; hence, to accuse; to impeach.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Implead \Im*plead"\, v. i.
   To sue at law.
   [1913 Webster]