In Japanese when there is more than one Samurai, there is a term indicating that as well, and its only the English way of doing so is by putting an "s" so I don't see what's wrong with it.
As hwoosh said, ususally you don't add something to indicate you mean more than one of something. There are words you can use to indicate you mean more than one of something, but Japanese is a very, you could say, lazy language. If you don't have to indicate or specify something, you usually don't in Japanese. That's why one of the first thing you learn when learning Japanese is how important context in Japanese is.
For example, just [ Taberu ] , which can mean [ I eat / he/she eats / they eat / I will eat / he/she will eat / they will eat ], is a perfectly valid sentence. Yup, many Japanese sentences only use one verb. Only context will tell you what exactly is meant. The same goes for numbers. If you want to say [ A samurai eats sushi ] or [ The Samurais eat sushi ], in both cases you'd say (if speaking to a friend): [ Samurai ha sushi o taberu] . Only context will tell you if one Samurai, or many are meant. You can, if absolutely necessary, specify you mean many Samurai, but if it isn't extremely crucial that the one you say it to knows you actually mean many and not just one (like, when your life depends on it), you don't do that in Japanese.
So I am interested, what word exactly do you mean?
