Abarim Publications' online Biblical Hebrew Dictionary
The masculine noun זהב (zahab) is the common Hebrew word for gold. This noun is assumed to derive of a verb זהב (zhb), but it's not clear what that verb might have meant. Our word is used to describe gold-ore (Genesis 2:11) but mostly as unit or manifestation of wealth (Genesis 13:2, Numbers 7:14) or trade or merchandise (Ezekiel 27:22). It's obviously also used frequently as embellishment or ornamentation (Genesis 24:22, 1 Samuel 6:4).
Because we are not sure what the root-verb of our noun might have meant, we can't be sure whether the gold-oil that Zechariah mentions is called such because it had a gold color (as suggested by BDB Theological Dictionary), or whether it was very costly, very pure or perhaps very difficult to make (Zechariah 4:12).
Gold was erroneously deemed worthy of worship (Exodus 32:3-4), even though YHWH was described as to appear in golden splendor (Job 37:22). The Psalmist asserts that the words of YHWH are to be considered better than gold (Psalm 19:10, 119:72), and Jesus explains that although gold is great, it derives its greatness from something greater: the temple sanctifies the gold and not vice versa (Matthew 23:17).
Gold items were valuable but gold also held an enormous value to the wisdom tradition. Very long ago observers noted that gold is the only substance known to man that doesn't transmute into something else. And since everything else, sooner or later, changes into something else, gold was seen as the ultimate result of all change: perfection, in one word. Gold held that status until the Word of the Lord came along (or rather: descended from where it had always existed) and surpassed the extent of natural evolution.
Another, less frequently used word for gold is פז (paz), probably denoting gold leaf.