I'm a former Airman who worked beside Soldiers, Sailers, and Marines. I don't know about proper definitions, but individually and generically, we were "troops." When our supervisors would talk about their supervisees, they would refer to us as their "troops." It's not a recent term. Go back to Viet Nam news reports, and they talk about "number of troops killed." A Soldier is widely considered as someone in the Army. According to the Oxford American Dictionary: "Troops -- soldiers or armed forces (UN peacekeeping troops)."

This is how it was described to me by one of my etymological professors.

This is a very rough explanation. We had a very interesting lesson on it. I just woke up. So, this is short.

When Europe was speaking older Indo-European languages, they had their own sets of words for things. When English became an established language, some of the Indo-European words stuck, some of them that were very descriptive and to the point. But it became prohibited to use these words. Kids, not understanding the difference between an allowed descriptive and a disallowed discriptive, would go to his mom and say, "I need to take a shit," or, "My ass itches." They would get in trouble for using the Indo- words. Voila, a dirty word.