astute, sharp, shrewd
Meaning: marked by practical hardheaded intelligence; "a smart businessman"; "an astute tenant always reads the small print in a lease"; "he was too shrewd to go along with them on a road that could lead only to their overthrow"
Had his astute mind guessed the secret, then?
He had come close enough for that astute individual to make out that he wore the same uniform young Gladwin had been masquerading in and he made capital of this on the instant.
Lorquas Ptomel was too astute an old warrior to be caught upon the open plains with a caravan of chariots and children, and so we remained at the deserted city until the danger seemed passed.