Words related to *ak-
late 14c., originally of fevers and diseases, "coming quickly to a crisis" (opposed to chronic), from Latin acutus "sharp, pointed," figuratively "shrill, penetrating; intelligent, cunning," past participle of acuere "to sharpen" (literal and figurative), from PIE root *ak- "be sharp, rise (out) to a point, pierce."
It was also used of humors (early 15c.). The meaning "ending in a sharp point" is from 1560s; the sense of "sharp or penetrating in intellect" is from 1580s. Of feelings, pains, etc., "intense," 1727. As a noun, early 15c. of fevers; c. 1600 as "an acute accent." Related: Acutely; acuteness.
also aiglet, "metal tag of a lace," meant to make it easier to thread through the eyelet-holes, but later often ornamental, mid-15c., from Old French aiguillette, diminutive of aiguille "needle," from Late Latin acucula, an extended form (via diminutive suffix, but not necessarily implying smallness) of Latin acus "a needle" (from PIE root *ak- "be sharp, rise (out) to a point, pierce"). Compare Italian agucchia, Portuguese agulha, Spanish aguja "needle."
order of lobe-finned fishes, 1850, from Modern Latin Coelacanthus (genus name, 1839, Agassiz), from Greek koilos "hollow" (from PIE root *keue- "to swell," also "vault, hole") + akantha "spine" (from PIE root *ak- "be sharp, rise (out) to a point, pierce"). So called from the hollow fin rays supporting the tail in fossil remains.
Thought to have gone extinct 66 million years ago until a living one was fished up off the east coast of South Africa Dec. 22, 1938. The specimen was noticed by museum curator Marjorie Courtney-Latimer, who wrote a description of it to South African ichthyologist J.L.B. Smith.
I stared and stared, at first in puzzlement. I did not know any fish of our own, or indeed of any seas like that; it looked more like a lizard. And then a bomb seemed to burst in my brain, and beyond that sketch and the paper of the letter, I was looking at a series of fishy creatures that flashed up as on a screen, fishes no longer here, fishes that had lived in dim past ages gone, and of which only fragmentary remains in rock are known. [J.L.B. Smith, "Old Fourlegs: The Story of the Coelacanth," 1956]
late 13c., "strenuous, ardent, fierce, angry," from Old French aigre "sour, acid; harsh, bitter, rough; eager greedy; lively, active, forceful," from Vulgar Latin *acrus (source also of Italian agro, Spanish agrio), from Latin acer "keen, sharp, pointed, piercing; acute, ardent, zealous" (from PIE root *ak- "be sharp, rise (out) to a point, pierce").
Meaning "full of keen desire" (early 14c.) seems to be peculiar to English. The English word kept a secondary meaning of "pungent, sharp-edged" till 19c. (as in Shakespeare's "The bitter clamour of two eager tongues," in "Richard II"). Related: Eagerly; eagerness. Eager beaver "glutton for work" [OED] is from 1943, U.S. armed forces slang.