Concise Bible Dictionary:
1. ἀρχηγύς; “beginner, leader.” It is “prince” in Acts 3:15 (“author” in the margin), the Lord Jesus is the originator of life. In Hebrews 12:2, the Lord Jesus is the “leader” and completer of faith: He began and finished the whole course. In Heb. 2:10 it is “captain” in the AV (KJV), He was “leader” of their salvation through suffering.
2. αἴτιος, “cause, occasion.” The Lord Jesus became the “author of eternal salvation” (Heb. 5:9).