Clinical NLP for Brazilian Portuguese remains limited by the lack of semantically structured resources that support interoperability and downstream health applications. Although existing corpora provide annotated clinical narratives, their flat annotation schemes restrict semantic expressiveness and alignment with standardized terminologies. In this work, we present a lightweight domain ontology that models clinical entities, contextual qualifiers, and semantic relations in Brazilian Portuguese texts. The ontology is derived from the original corpus annotations and conceptually aligned with standards to enhance interoperability while preserving corpus-specific semantics. This work establishes foundational infrastructure for Portuguese clinical NLP, supporting tasks such as entity normalization, semantic search, and ontology-guided annotation.