What is Acute?

Acute definition and meaning on Dictionary terms:
sharp or severe in effect; intense: acute sorrow; an acute pain.
extremely great or serious; crucial; critical: an acute shortage of oil.
(of disease) brief and severe (opposed to chronic).
sharp or penetrating in intellect, insight, or perception: an acute observer.
extremely sensitive even to slight details or impressions: acute eyesight.

sharp at the end; ending in a point.
Geometry. (of an angle) less than 90