The Collaborative International Dictionary of English v.0.48:

Obturate \Ob"tu*rate\, v. t. [imp. & p. p. Obturated; p. pr. &
   vb. n. Obturating.] [L. obturatus; p.p. of obturare.]
   To stop or close, as an opening; specif., (Ordnance), to stop
   (a gun breech) so as to prevent the escape of gas in firing.
   [Webster 1913 Suppl.]