acute

extremely sharp or severe

“acute pain”

having or demonstrating ability to recognize or draw fine distinctions

“an acute observer of politics and politicians”

ending in a sharp point

a mark placed above a vowel to indicate pronunciation

having or experiencing a rapid onset and short but severe course

“acute appendicitis”

of critical importance and consequence

“an acute (or critical) lack of research funds”

of an angle; less than 90 degrees