irreptitious

from The Collaborative International Dictionary of English v.0.48

Irreptitious \Ir`rep*ti"tious\, a. [L. irrepere, irreptum, to
   creep in; pref. ir- in + repere to creep.]
   Surreptitious; spurious. [Obs.] --Dr. Castell (1673).
   [1913 Webster]