Sentence:  Sunning himself on the board steps, I saw for the first time Mr. Farquhar Fenelon Cooke....A silver snaffle on a heavy leather watch guard which connected the pockets of his corduroy waistcoat, together with a huge gold stirrup in his Ascot tie, sufficiently proclaimed his tastes....But withal there was a perceptible <WSD>acumen</WSD> about the man which was puzzling in the extreme. 
Meaning of the word marked with <WSD> tags:  Quickness of perception or discernment; penetration of mind; the faculty of nice discrimination.