Synonyms for Shrewd (same or very similar meaning)
WordNet sense 1 (used of persons):
calculating, calculative, conniving, schemingWordNet sense 2 (dispassionate):
hardWordNet sense 3 (marked by practical hardheaded intelligence):
astute, sharpWordNet sense 4 (showing mental alertness and calculation and resourcefulness):
smartFrom the ODE community, based on WordNetadd/edit