Good morning, Netizens…
The student's vacuous facial expression suggested a lack of comprehension.
“When the leaves begin to turn and the temperature calls for long sleeves, we stow the whites and rosés in favor of reds. It's easy but vacuous logic. Color is not the most significant factor in drinking [wine] seasonally. It's texture and weight.” — From an article by Eric Asimov in the New York Times, October 24, 2012
As you might have guessed, “vacuous” shares the same root as “vacuum”—the Latin adjective “vacuus,” meaning “empty.” This root also gave us the noun “vacuity” (the oldest meaning of which is “an empty space”) as well as the verb “evacuate” (originally meaning “to empty of contents”). Its predecessor, the verb “vacare,” is also an ancestor of the words “vacation” and “vacancy” as well as “void.” All of these words suggest an emptiness of space, or else a fleeing of people or things from one place to another. “Vacuous” appeared in English in the middle of the 17th century, at first literally describing something that was empty. It acquired its figurative usage, describing one who is lacking any substance of the mind, in the mid-1800s.