The Collaborative International Dictionary of English v.0.48:

Imbosk \Im*bosk"\, v. t. [imp. & p. p. Imbosked; p. pr. & vb.
   n. Imbosking.] [CF. It. imboscare to imbosk, imboscarsi to
   retire into a wood; pref. im- in + bosco wood. See Boscage,
   and cf. Ambush.]
   To conceal, as in bushes; to hide. [Obs.] --Shelton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Imbosk \Im*bosk"\, v. i.
   To be concealed. [R.] --Milton.
   [1913 Webster]