Right, right... must remember...

[xyzzysqrl]

...the plural of ninja is ninja.
...the plural of samurai is samurai.
...the plural of ninja is ninja.
...the plural of sumo is sumo.
...the plural of ninja is ninja.

Comments

[terrycloth.livejournal.com]

According to dictionary.com, Random House and American Heritage both think 'ninjas' is an acceptable alternate plural.