shrewd: [14] Shrewd originally meant ‘wicked, dangerous’. Its modern sense ‘astute’ did not develop (via a less approbatory ‘cunning’) until the 16th century. It was derived from shrew ‘wicked man’ (a sense now obsolete). This is generally assumed to be the same noun as shrew the animal-name [OE], a word of uncertain origin. Shrews were formerly thought to have a poisonous bite, and were held in superstitious fear – hence the term’s metaphorical application. The move from ‘wicked man’ via ‘bad-tempered abusive complainer’ to ‘nagging woman’ began in the 14th century. => shrew
