You may need a battery of dictionaries to get all the answers.
Colonel derives from the the Latin, "columna" or column. Old italian is "colonello", a dimunitive of "colonna" a column of soldiers.
A cornet is at once a small crown, indicative of minor nobility or the junior officer in a mounted organization, ranking below a second lieutenant, who carried a musical instrument. His infantry equivalent was an ensign, who carried a flag.
See the "American Heritage College Dictionary, 3rd Edition" and "The Continental Army" by Robin K. Wright.
You are correct on lieutenant. A subaltern is lower in position or rank and the usage is chiefly British although the 2nd Cavalry once had a Subaltern's Shoot for armored cavalry platoon leaders (and may still).
Sergeant once meant in Middle English common soldier ("sergeaunte")
For the rest, you're on your own,
James B. Ronan II
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