BackgroundThe phenomenon of ‘moral distress’ has continued to be a popular topic for nursing research. However, much of the scholarship has lacked conceptual clarity, and there is debate about what it means to experience moral distress. Moral distress remains an obscure concept to many clinical nurses, especially those outside of North America, and there is a lack of empirical research regarding its impact on nurses in the United Kingdom and its relevance to clinical practice.Research aimTo explore the concept of moral distress in nursing both empirically and conceptually.MethodologyFeminist interpretive phenomenology was used to explore and analyse the experiences of critical care nurses at two acute care trauma hospitals in the United Kingdom. Empirical data were analysed using Van Manen’s six steps for data analysis.Ethical considerationsThe study was approved locally by the university ethics review committee and nationally by the Health Research Authority in the United Kingdom.FindingsThe empirical findings suggest that psychological distress can occur in response to a variety of moral events. The moral events identified as causing psychological distress in the participants’ narratives were moral tension, moral uncertainty, moral constraint, moral conflict and moral dilemmas.DiscussionWe suggest a new definition of moral distress which captures this broader range of moral events as legitimate causes of distress. We also suggest that moral distress can be sub-categroised according to the source of distress, for example, ‘moral-uncertainty distress’. We argue that this could aid in the development of interventions which attempt to address and mitigate moral distress.ConclusionThe empirical findings support the notion that narrow conceptions of moral distress fail to capture the real-life experiences of this group of critical care nurses. If these experiences resonate with other nurses and healthcare professionals, then it is likely that the definition needs to be broadened to recognise these experiences as ‘moral distress’.