6G networks intend to be highly dynamic, automated, and distributed while enabling novel user-centric services, which has raised the attention to trustworthiness aspects. In this context, trustworthiness has been pointed out as a key driver for the development of 6G technology. However, a common understanding of the definition and extension of trustworthiness is still missing in the community. Therefore, this paper aims at providing critical definitions for trustworthiness to steer the development of 6G by building upon 3 pillars: trustworthiness attributes, context, and assessment. First, we provide a comparative study of attributes for trustworthiness and identify the set of self-contained attributes that allow for a quantitative characterization of trustworthiness in 6G systems. Then, we recognize and discuss the main misconceptions regarding trustworthiness in the context of 6G and propose an assessment framework of two components for trustworthiness evaluation. This framework includes a numerical scaling of relevance of attributes, a scoring system, and a labeling approach to admit flexibility to identify a degree of trustworthiness evaluation for different capabilities in 6G.