sanmai

Etymology
, literally, 3 sheets

Noun

 * 1)  A construction method for Japanese-style blade steels, usually sandwiching a hardenable steel in a taco of flexible steel, that is forge-welded together, leaving a hardenable edge steel and flexible spine steel, for single-edged blades.
 * 2)  A steel sandwich made by this method, before and after being welded.