In the modern world, connectivity and shared intelligence enable independent constituent systems (CS) to form systems of systems (SoS) capable of performing sophisticated missions. However, the sheer scale of an SoS can make it challenging to manage all components comprehensively, hiding potential security and safety concerns. These factors underscore the need for advancing conceptual models that permit a better understanding of the SoS intricacies. This paper presents a conceptual model for an integrated safety-security ontology for SoS, called SSO-SoS. Such a model is based on international standards, existing literature, and relevant conceptual models, where we pay special attention to safety, security, and mitigation for SoS. We also illustrate the SSO-SoS with a case study from the construction sector. Our conceptual model provides a hierarchical organization that permits stakeholders to navigate through different layers of information, enhancing their ability to identify, address, and understand the required SoS knowledge.