Final answer:
The adjective 'radial' is used to describe anything related to the radius bone in the forearm, equivalent to how 'humeral' pertains to the humerus.
Step-by-step explanation:
The adjective that means pertaining to the radius is "radial".
Similar to how "humeral" pertains to the humerus, "radial" is used to describe anything related to the radius bone located along the lateral (thumb) side of the forearm.
This term is particularly relevant when discussing parts of the forearm in anatomy or when referring to injuries, such as a fracture that affects the radiocarpal joint of the wrist.
For example, a radial fracture refers to a break in the radius bone, which may involve the joint surface disrupting the articulation with the humerus at the elbow or with the carpal bones at the wrist.