(verb)
to provide medical care and treatment to someone in poor health, especially as an occupation;
e.g. He helped to nurse his mother back to health. She was hired to nurse in the emergency department of the hospital.
(verb)
broadly, to be protective and/or careful in handling something, either literally in order to treat an injury or figuratively in order to protect something's well-being;
e.g. She didn't want to nurse a sprained ankle while on vacation.
(verb)
to hold on to something for a relatively long period of time, for example to have some feeling or belief for a long time or to take occasional sips from the same drink for a long time;
e.g. They started to nurse a hatred for him because of his rudeness. I tend to nurse the same cup of coffee all through the morning.
(verb)
to feed a baby with breast milk, or to be thus fed with breast milk;
e.g. She went into a different room to nurse her crying baby.