except, besides: marking the one person or thing left out of what is said about all the rest
This is a small word with one job: it carves out an exception. Something is said about a whole group, or a whole class of things is denied, and this word names the one that falls outside it. Joshua burned none of the cities that stood on their mounds, except Hazor. All Israel went over to Jeroboam, except the tribe of Judah. There was no stranger in the house, except the two women themselves.
It turns up in only sixteen verses, and it nearly always has a short ending attached, so that it looks like "except me" or "besides you." Sometimes that is exactly what it means, as when God says that no other god stands besides him. But often the ending is not a pronoun at all, and the word simply means "except," with the thing excepted named right after it: at the mountain the people saw no shape, only a voice (Deuteronomy 4:12), and the psalmist asks who is a rock except our God (Psalm 18:31).
The second way it works is to rule out any rival. A whole class is denied, and then the one named is set over against it: no God besides you, no rock except our God, no other sword besides this one, no kinsman besides you with the right to buy back the land. That wording is ordinary Hebrew, used of a sword and a relative as readily as of God, and it is the frame that carries some of the Old Testament's sharpest claims that the LORD alone is God.
Hebrew has a small family of words for "except" and "without," and two verses set this one right beside another of them. Psalm 18:31 asks who is God apart from the LORD (בִּלְעֲדֵי) and who is a rock except our God, and Hosea 13:4 says there is no God besides me and no savior but me (בִּלְתִּי). The two words are close enough in force that the writers seem to be varying them for the sake of the poetry rather than drawing a distinction.