Certain nursing educators are acquiring this word and using it to mean "intensity of nursing care or medical intervention required". You can see the thinking: an acute care patient needs more than a chronic care patient, who needs more than a nursing-home patient. But for their own convenience, they have decided that acuity is a measure of the level of scute illness the patient has, rather than its true meaning.
It's funny how much new jargon is introduced by educationalists, who really should be defending the precision of language, rather than diluting it. Another example is the term "competency", which is a unit of skill that is acquired and can be measured after a given educational or training exercise. Regrettably, it is often confused with "competence", which simply means ability to do the job one is appointed to do, the reverse of incompetence.