You bring up a good point of discussion: words with multiple meanings. Such words exist in the Old and New Testaments.
Eternal is one such word. It can mean "until the end of the age" or "from age to age" or "from age to age for endless ages". It can also define the origin of another thing like saying "southern sandwich". The origin of the sandwich, or at least its character, is derived from a place in the south. "Eternal life" for example, originates in "eternity" and it also possesses the characteristics of eternity: it's a life that was eternally in God and a life that will never pass away.
World is like this. We know that we are to be like God. we are told "God so loved the world" but then we are told "Love not the world". Same word. One, we know to mean people, the other, we know to mean systems.
And here's the catch: in order to know the meaning of the these types of words one must know the One who wrote them. This requires revelation by the spirit in us from the Spirit who wrote the words. A doctorate in etymology will not help you know God. Revelation, the Holy Spirit to man's spirit, is the only way.
For example, if you found a letter written by my wife to me and you had it examined by the most prestigious language professors in the world and they concluded that my wife meant "thus and such" by her letter BUT then I read the letter and I say "No, she does not mean "thus and such", she means "this". Who will you believe? Well, you should believe the one who knows my wife the best: me. I know her idiosyncrasies, her desires, the pattern of her words and so on. No amount of education in language can help you know my wife.
That's enough for now.