What do we call an organism, typically a parasite, that ultimately kills its host?

The term "parasitoid" is used to describe an organism, often a type of insect, that lives in or on a host and ultimately leads to the host's death. This relationship is distinct from that of a typical parasite, which generally does not kill its host. Parasitoids often undergo a developmental stage within the host, feeding off its tissues until they emerge as adults, thereby causing the host to perish in the process.

In contrast, a pathogen typically refers to any organism, such as bacteria or viruses, that causes diseases but does not necessarily kill its host. Nematodes can be either beneficial or harmful, and while some are parasites, not all of them are parasitoids. Beneficial insects, on the other hand, contribute positively to the ecosystem, such as pollinators or natural pest controllers, without causing harm to their hosts. Thus, the most accurate term for an organism that ultimately kills its host is parasitoid.