a number: the count or total you get when you add up how many of something there are
At its heart this word names the result of counting. When a group is tallied up, the figure that comes out is its number, and that is what this word points to: the count of soldiers in an army, of people in a census, of years in a span, of days that remain. It is not the act of counting (that is the verb it comes from) but the answer the counting produces.
From that core, two opposite turns of phrase grew up around it, and they account for most of the colorful uses. Because a thing that can be counted is by definition limited, the phrase "men of number" came to mean a handful of people, so few you could quickly count them. And because the way to say something is past counting was to say it has "no number," the word also sits at the center of the great pictures of multitudes too vast to tally: locusts, sand on the seashore, the stars, the troubles that overwhelm a person.
So a single plain idea, the figure you reach by counting, stretches in everyday Hebrew from "only a few" all the way to "beyond all counting," depending on whether the count is small, stated, or flatly denied.