The word "不少" is formed by directly combining the negative prefix "不" (not) with the adjective "少" (few; little). This creates a logical and intuitive semantic unit where the negation of "few" results in the meaning "not few", which is understood to mean "many" or "a considerable number". It is a straightforward example of conceptual compounding, where the meaning of the whole is derived from the simple, literal negation of its second component.