A nurse was an independent health care practitioner who, along with a doctor, was responsible for an individual's health and well-being.
Most nurses wore a uniform, whether one for nursing in general or, if they belonged to a military (such as the US Army (Garland) or Starfleet (Christine Chapel)), the appropriate divisional and rank attire and insignia. One who took on the role of a nurse while caring for another could be said to have "nursed" them "back to health". (TAS: "The Survivor"; TNG: "Unification I", "Descent", "Liaisons")
Some nurses specialized in certain fields, as doctors did. Beck, for example, was an obstetrics specialist. (TNG: "Lessons")
Dr. Leonard McCoy found nurses easier to work with than other doctors, remarking that another doctor would "argue every little diagnosis with me." (Star Trek: The Motion Picture)
In 2293, Commander Pavel Chekov "drafted" three journalists as nurses to help care for the injured El-Aurian refugees in the unstaffed sickbay of the USS Enterprise-B. (Star Trek Generations)
In 2369, the Bajoran farmer Mullibok called Kira Nerys his nurse when she cared for him after he was shot by a Bajoran phaser. (DS9: "Progress")
When Julian Bashir asked Yeto to help him treat Quark's injuries in 2370, he initially balked, saying he was not Bashir's nurse. (DS9: "Invasive Procedures")
In 2374, The Doctor asked Seven of Nine to play the part of the doctor while he played the role of the nurse in a conversational exercise entitled "The Workplace Encounter". (VOY: "Prey")