What term describes a characteristic that is derived and unique to one or more organisms in a clade?

The term that best describes a characteristic that is derived and unique to one or more organisms in a clade is "apomorphic." Apomorphy refers to a derived trait that distinguishes a particular lineage from its ancestors. This trait evolves after the divergence from a common ancestor, providing important information for understanding evolutionary relationships within a clade.

In contrast, synapomorphism is a specific type of apomorphy that is shared by two or more taxa and is derived from a common ancestor, suggesting a common evolutionary path. While homologous traits indicate similarities due to shared ancestry, analogous traits arise independently in different lineages, often as adaptations to similar environments or challenges, and do not provide information about shared ancestry. Thus, focusing on the uniqueness of derived traits within a clade emphasizes the role of apomorphic characteristics in defining evolutionary relationships.