From Latin 'acuere' (to sharpen) — mental sharpness, from the same PIE root as 'acute' and 'acid.'
The ability to make good judgments and quick decisions, especially in business.
From Latin acūmen (a sharp point, the sharpness of a weapon or wit, mental keenness, acuity), from acuere (to sharpen, to make pointed), from acus (needle, pin, pointed instrument), from PIE *h2ek- (sharp, pointed, at the peak). The PIE root *h2ek- is one of the most productive in the family: it gives Latin acer (sharp, keen, eager), acies (sharp edge, line of battle), acid (via acēre, to be sharp-tasting), acne (via Greek akne, pointed eruption), acorn (via Old English æcern, from the pointed Germanic cognate), and oxygen (via Greek oxy-, sharp, acid). English acumen entered in the 16th century directly from Latin rhetorical
Intelligence was metaphorically 'sharp-wittedness.'