Clinical Trial as the pillar.

Reasons:

• Search demand: “clinical trial” is searched far more frequently than “clinical study.”
• Audience expectations: Junior CRAs, CRCs, investigators, and sponsors overwhelmingly use “clinical trial” in day-to-day work.
• Regulatory prominence: ICH E6(R3), EU CTR 536/2014, FDA guidance, and many other regulatory documents are centered on clinical trials.
• Internal linking: Most of your glossary naturally relates to trials (protocol, CRF, monitoring, SAE, ADR, audit, investigator, sponsor, etc.).

Then make Clinical Study a supporting