Senshi
戦士
Warrior, fighter.
Examples
In Bishoujo Senshi Sailor Moon the term is often translated as "soldier" or even "guardian".
Kanji
戦 Sen means "war" or "battle". Is also the first kanji in "Sentai".
士 Shi means "warrior" or "samurai" or "gentleman". Note the line on top is longer than the one on bottom. If the line on top is shorter, it becomes the kanji for "ground".