How did 'acute' evolve to mean 'quick'?

Question

[1.] [OED:] acute, adj.    [=]    A. adj. 1. Med.
a. Of a disease, symptom, etc.: coming quickly to a crisis or conclusion; of rapid onset and short duration; of recent or sudden onset; contrasted with chronic adj. 2a; cf. subacute adj. 2.
In similar contexts: severe; critical. Also in figurative context.

[2.] Etymology: < classical Latin acūtus  [=]  sharpened, pointed, sharp, tapering, having sharp needles, keen, discriminating, keen-witted, shrewd, nimble, quick, pungent, acrid, high-pitched, piercing, shrill, treble, ...

[3.] [Etymonline:] late 14c., originally of fevers and diseases, "coming and going quickly"
(opposed to a chronic), from Latin acutus "sharp, pointed," figuratively "shrill, penetrating; intelligent, cunning," past participle of acuere "sharpen" (see acuity). ...

How did the Latin acuere "sharpen" evolve into definition [1.] above for 'acute'?
Sharpness can be quick or long. So how does sharpen connect with quick?

I am confused because OED states this definition for quickness for the Latin acūtus, but Etymonline doesn't broach quickness until the later reference to fevers and diseases.

Footnote: I read this other post on 'acute'.

Answer 1

The imagery of sharp, which is the root of acute can easily expand to include quick in the mind of any astute observer:

1) Semantic Expansion ... a word increases its range of meaning over time ... horn ‘bone-like protrusion on the heads of certain animals’, then ‘musical instrument’, then ‘drinking vessel’ of similar shape. The instance of arrivare just quoted belongs to this category.

_{Types of Semantic Change}

arrive (v.)
c. 1200, "reach land, reach the end of a journey by sea,"
from Anglo-French ariver, Old French ariver (11c.) "to come to land,"
from Vulgar Latin arripare "to touch the shore,"
from Latin ad ripam "to the shore,"
from ad "to" (see ad-) + ripa "shore" (see riparian).
The original notion is of coming ashore after a long voyage. Of journeys other than by sea, from late 14c. Sense of "to come to a position or state of mind" is from late 14c. Related: Arrived; arriving.

_{etymonline.com}

People notice a dull knife cuts through things slowly with great effort, while a sharp knife cuts through things quickly with minimal effort. People notice that a sharp mind cuts through problems to solutions more quickly. People notice a sharp eye focuses on the essential shapes more quickly. Eventually, the persistent association of quick in the mind of the observer connects itself to the word acute, which was borrowed from Latin by doctors specifically to describe a disease that harmed a body more quickly.

Answer 2

"acute" has no connection to "quick".

Your reading of "definition 1" is completely wrong.

Acute essentially means "sharp" or "strong".

Note that in the OED description which reads "coming quickly to a crisis or conclusion" ...

... consider a very sharp blade, we're looking at it's cross section in close-up. You would describe the "hill" of the blade as ... "coming quickly to a point". But that does not mean "sharp" has anything to do with "quick". It's just that the word "quick" is being used in that description.

Let's say the OED description had read "of a disease, going from nothing to maximum in only a few days". You would not then say "how does acute mean few days".

Acute is just the latin word for sharp .. it's that simple.

Answer 3

I can try to give you my interpretation from a medical professional view as well as a linguistic enthusiast view. I'm going to steal Law Area 51's OED and Etymology portions.

[1.] [OED:] acute, adj.    [=]    A. adj. 1. Med. a. Of a disease, symptom, etc.: coming quickly to a crisis or conclusion; of rapid onset and short duration; of recent or sudden onset; contrasted with chronic adj. 2a; cf. subacute adj. 2. In similar contexts: severe; critical. Also in figurative context.

[2.] Etymology: < classical Latin acūtus  [=]  sharpened, pointed, sharp, tapering, having sharp needles, keen, discriminating, keen-witted, shrewd, nimble, quick, pungent, acrid, high-pitched, piercing, shrill, treble, ...

Acute describes a sharp slope of progression and regression (similar to the "shape" of an acute angle). This is the reason for the use of "acute" to describe an illness that has a sudden onset and rapid recovery. Acute gastroenteritis begins in a matter of minutes and lasts only 12-36 hours.

Acute things are pointed, sharp, discriminating, severe, critical. This is the reason for the use of "acute" to describe an illness that is very severe in nature or effect. Acute hemorrhage is severe because it is sudden and discriminatory in it's nature (that phrase only describes rapid blood loss). Acute abdominal pain is discriminating and sharp pain causing severe discomfort.

So those are my attempt at explaining the use in medical jargon.