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). Meaning "sharp, irritating" is from early 15c. Meaning "intense" is from 1727. Related: Acutely; acuteness.