there is not: the word that denies that something exists or is present
This is Hebrew's main way of saying that something simply is not there. Where English says "there is" to assert that a thing exists, Hebrew uses this word to say the opposite: there is no such thing, none of it is here, it does not exist. It is the flat denial of being or presence.
Its senses are not different words but one idea worn into different shapes by the sentence around it. On its own it announces that something is missing or nonexistent ("there is no water," "she had no child"). With a personal ending attached it denies a person or thing in particular ("he is not here," "I am not"). Standing alone as a thing in itself it means "nothing, nothing at all," the way the prophets say the nations amount to nothing before God. And in fixed phrases it works like the English "without": without number, without a shepherd.
What ties all of this together is a single move: the speaker reaches for something expected, a person, an object, a possibility, and reports that it is not to be found. That is why one small word does so much work across the whole Hebrew Bible.
It is the exact mirror image of the word that asserts existence, "there is" (yesh). Where that word says a thing is present, this word says it is absent. The two are a matched pair, the yes and the no of existence in Hebrew.