Commander, Commander In Chief, Team Captain
noun
The master commander is the commander of all commanders, the commander in chief if you will... or, even the team captain.
しゅしょう
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
どちらの主将もそんなに強くはなかった。
Neither of the team captains was very strong.