The idea of solidarity is in vogue, especially since the eruption of the COVID-19 pandemic. However, the term “solidarity,” as used in nursing, is imprecise and vague, lacking clear definition and connoting a variety of general meanings. Based on the original meaning of “solidarity” in ancient Roman law, this article captures the archetypical idea of solidarity from a historical and interdisciplinary perspective. This archetypical or primary meaning comes before the development of any other meanings of the word, and it is (...) therefore authentic and genuine because it does not derive from something else. After establishing the archetypical meaning of solidarity, the article translates this meaning into the area of nursing and demonstrates a deep connectivity between healthcare and solidarity. The second part of the article offers and develops a new definition of nursing solidarity as the responsibility for the healthcare of a person (unit) shared as a whole (entirety) by that person and a nurse or a nursing team (plurality). This new definition has some implications for nursing practice and education, since the definition emphasizes the idea that solidarity helps to (a) foster respect and avoid discrimination, (b) promote cohesion in health communities, (c) increase individual responsibility and a spirit of service, (d) stimulate motivation, (e) improve communication, (f) create an engaging workplace, and (g) develop leadership. (shrink)