Step 1: Recall the defining feature of a tribe:
A tribe is generally defined by a distinct territory, common ancestry/kinship, and a way of life outside the caste hierarchy.
Step 2: Test each name against that feature:
Bhil, Gond and Tharu all meet this definition and appear on India's Scheduled Tribes lists. Namboodiri, by contrast, is a caste group occupying the priestly (Brahmin) position within the caste hierarchy - the opposite of a tribe existing outside that hierarchy.
Final Answer:
Namboodiri (Option D)