anything: an unspecified single thing, which in the negative sentences where it usually appears means nothing at all
This is a stand-in word, like English "anything." It does not name a particular object; it points at some unspecified thing, a single item of any kind. Its force depends entirely on the sentence around it.
In a plain or questioning sentence it means "anything, something": may I say anything, will you lend anything, could he do anything. But the word turns up most often inside a denial, and there English says "nothing." That negative is not hidden in the word itself; it comes from the "not" standing next to it, exactly as English "he did not do anything" collapses into "he did nothing."
When it does appear in a denial, it tends to sweep the whole field: not one thing, nothing whatsoever. Joseph kept back nothing at all from his master; the master worried about nothing at all in the house. That total, emphatic reach is the flavor the word carries, whichever way an English sentence phrases it.