From the Bible, we have inherited a few interesting phrases with the word double in it. Two examples are a double heart and a double mind. Merely hearing the phrase leads one to think that a double heart refers to a person whose heart is moving in two different directions. And that would be quite close to its meaning as it appears in the Bible.
Psalm 12:2—"Everyone utters lies to his neighbor; with flattering lips and a double heart they speak."
In Hebrew, the literal expression is "a heart and a heart". It means someone who is capable of double-crossing and lying. I find that expression very interesting. Likewise, when the Bible speaks of differing weights in Deuteronomy in 25:13, the Hebrew phrase is literally "a stone and a stone".
Deuteronomy in 25:13—"You shall not have in your bag two kinds of weights, a large and a small..."
Which leads me to wonder about the phrase "double-minded man" found in James 1:8.
James 1:8—"He is a double-minded man, unstable in all his ways."The book of James was written in Greek, but perhaps the Hebrew style of using the word twice when a contradiction or contrast was needed was carried over. I'll need someone with more expertise in Koine Greek to confirm this.

