Easton's Bible Dictionary
A word of Anglo-Saxon origin, and meaning "God's spell", i.e., word of God, or rather, according to others, "good spell", i.e., good news. It is the rendering of the Greek evangelion, i.e., "good message." It denotes (1) "the welcome intelligence of salvation to man as preached by our Lord and his followers.
(2.) It was afterwards transitively applied to each of the four histories of our Lord's life, published by those who are therefore called `Evangelists', writers of the history of the gospel (the evangelion).
(3.) The term is often used to express collectively the gospel doctrines; and `preaching the gospel' is often used to include not only the proclaiming of the good tidings, but the teaching men how to avail themselves of the offer of salvation, the declaring of all the truths, precepts, promises, and threatenings of Christianity." It is termed "the gospel of the grace of God" (Acts 20:24), "the gospel of the kingdom" (Matthew 4:23), "the gospel of Christ" (Romans 1:16), "the gospel of peace (Ephesians 6:15), "the glorious gospel," "the everlasting gospel," "the gospel of salvation" (Ephesians 1:13).
Noah Webster's New International Dictionary of the English Language
1. (v.) Glad tidings; especially, the good news concerning Christ, the Kingdom of God, and salvation.
2. (n.) One of the four narratives of the life and death of Jesus Christ, written by Matthew, Mark, Luke, and John.
3. (n.) A selection from one of the gospels, for use in a religious service; as, the gospel for the day.
4. (n.) Any system of religious doctrine; sometimes, any system of political doctrine or social philosophy; as, this political gospel.
5. (v.) Anything propounded or accepted as infallibly true; as, they took his words for gospel.
6. (a.) Accordant with, or relating to, the gospel; evangelical; as, gospel righteousness.
7. (v. t.) To instruct in the gospel.