Perspicacious
Definition: shrewd; showing intelligence or insight
Why I Looked It Up
In a discussion of Abigail Adams:
Abigail Adams is best known for her copious, perspicacious correspondence in which she discussed politics as well as domestic concerns.
Postscript
Added on
From Once Upon a Tome:
From his paper-strewn desk in a dimly lit corner of the shop he watched over the books, guarding them with a suspender-clad perspicacity cultivated over many years…