The Only Use of
bulwark
in
Hamlet, Prince of Denmark
-   sit you down,
 And let me wring your heart: for so I shall,
 If it be made of penetrable stuff;
 If damned custom have not braz'd it so
 That it is proof and bulwark against sense.†Scene 3.4
Definition:
something that offers protection -- especially a defensive wall or embankment, or a sea wall
or (especially in classic literature): the part of a ship's side that is above the upper deck
or (especially in classic literature): the part of a ship's side that is above the upper deck