The word 毒素 is formed through a direct and logical conceptual combination of its two component characters: 毒, which means "poison" or "toxic", and 素, which in this context means "element", "substance", or "basic constituent". It is not an abstract metaphor but a concrete compounding where the second element specifies the nature of the first; thus, a "poison-element" or "toxic substance" is understood as the inherent poisonous agent or toxin within something.