The word evangelion is common to both modern and ancient Greek and is derived from the prefix ev, more commonly transliterated "eu" (as in euphemism, eulogy etc.) which is used to denote something benign, and the ancient "angellein" which means to announce. Hence "angel" is merely Greek for harbinger and not some metaphysical jargon.
Literally, evangelion means good news. In common usage as well as in mediaeval and modern Greek, it means the gospel, which makes sense since Christians consider the gospel a good newsflash from God.