What is the correct root for underlined word captain leader of paratroopers?

The word "captain" in this context refers to a military leader and is derived from the Latin word "capitaneus".

"Capitaneus" means "head" or "chief" and is the origin of the English word "captain", which signifies a leader or commander.

Therefore, the correct root for the underlined word "captain" in this context is "capitaneus".