acute

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Reacting readily to stimuli or impressions; sensitive.
• adjective Keenly perceptive or discerning: synonym: sharp.
• adjective Extremely sharp or severe; intense.
• adjective Of great importance or consequence; critical.
• adjective Having a rapid onset and following a short but severe course.
• adjective Afflicted by a disease exhibiting a rapid onset followed by a short, severe course.
• adjective High in pitch; shrill.
• adjective Narrowly pointed; sharp.
• adjective Having an acute angle.

from The Century Dictionary.

• To render acute in tone.
• Sharp at the end; ending in a sharp point or angle: opposed to blunt or obtuse.
• Sharp or penetrating in intellect; possessing keenness of insight or perception; exercising nice discernment or discrimination: opposed to dull or stupid: as, “the acute and ingenious author,” Locke.
• Manifesting intellectual keenness or penetration; marked or characterized by quickness of perception or nice discernment: applied to mental endowments and operations: as, acute faculties or arguments.
• Having nice or quick sensibility; susceptible of slight impressions; having power to feel or perceive small or distant objects or effects: as, a man of acute eyesight, hearing, or feeling.
• Keen; sharp; intense; poignant: said of pain, pleasure, etc.
• High in pitch; shrill: said of sound: opposed to grave. See acute accent, below.
• In pathology, attended with more or less violent symptoms and coming speedily to a crisis: applied to a disease: as, an acute pleurisy: distinguished from subacute and chronic.
• A mark (′ ) used to denote accentual stress, and also for other purposes. To denote stress in English, it is now generally placed after the accented syllable, as in this dictionary, but sometimes over the vowel of that syllable. The latter is done regularly in such Greek words as take this accent, and in all Spanish words the accentuation of which varies from the standard rule. In some languages it is used only to determine the quality or length of vowel-sounds, as on e in French (as in été), and on all the vowels in Hungarian; and in Polish and other Slavic languages it is also placed over some of the consonants to mark variations of their sounds. For other uses, see accent, n.
• Keen may be the most objective of these words. An acute answer is one that shows penetration into the subject; a keen answer unites with acuteness a certain amount of sarcasm, or antagonism to the person addressed; a shrewd answer is one that combines remarkable acuteness with wisdom as to what it is practically best to say.
• Shrewd differs from acute and keen by having an element of practical sagacity or astuteness. Only keen has the idea of eagerness: as, he was keen in pursuit. See astute and sharp.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb rare To give an acute sound to.
• adjective Sharp at the end; ending in a sharp point; pointed; -- opposed to blunt or obtuse
• adjective Having nice discernment; perceiving or using minute distinctions; penetrating; clever; shrewd; -- opposed to dull or stupid
• adjective Having nice or quick sensibility; susceptible to slight impressions; acting keenly on the senses; sharp; keen; intense
• adjective High, or shrill, in respect to some other sound; -- opposed to grave or low.
• adjective (Med.) Attended with symptoms of some degree of severity, and coming speedily to a crisis; -- opposed to chronic.
• adjective (Geom.) an angle less than a right angle.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Urgent.
• adjective sensitive
• adjective Short, quick.
• adjective geometry Of an angle, less than 90 degrees.
• adjective geometry Of a triangle, having all three interior angles measuring less than 90 degrees.
• adjective botany, of leaves With the sides meeting directly to form a pointed acute angle at the apex, base, or both.
• adjective medicine Of an abnormal condition of recent or sudden onset, in contrast to delayed onset; this sense does not imply severity (unlike the common usage).
• adjective medicine Of a short-lived condition, in contrast to a chronic condition; this sense also does not imply severity.
• adjective orthography, after a letter Having an acute accent.
• noun orthography An acute accent.
• verb phonetics To give an acute sound to.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective extremely sharp or intense
• noun a mark (') placed above a vowel to indicate pronunciation
• adjective of critical importance and consequence
• adjective ending in a sharp point
• adjective having or experiencing a rapid onset and short but severe course
• adjective of an angle; less than 90 degrees
• adjective having or demonstrating ability to recognize or draw fine distinctions