a negative word meaning not, except, or so that not; it cancels or limits whatever follows it
This is one of Biblical Hebrew's negative words, and like the English word "not" it does most of its work by attaching to something else and shutting it down. What it shuts down decides how we translate it. Joined to a verb, it blocks the action ("so that they would not eat"). Standing after a denial, it carves out the one exception to that denial ("you shall not see my face, except your brother is with you"). Set beside a quality, it simply reverses it ("not clean"). And set beside a name, it shuts out every rival ("there is none besides you").
The most common use by far attaches it to a verb to express a purpose or a result that is being avoided, the sense "in order not to" or "so that... not." Much of the time it carries the weight of a command or a warning: do this so that the bad thing will not happen.
Because its meaning shifts with what it negates, no single English word fits everywhere. "Not," "except," "save," "besides," and "so that not" are all the same Hebrew word doing the same basic job, blocking or limiting the thing next to it, just aimed at a different target each time. Readers should not hunt for a hidden meaning in the word itself; the meaning lives in what it is canceling.