'stern demeanor' is a correct and usable phrase in written English.
It can be used to refer to someone's behavior that is serious and looks intimidating. Example sentence: The principal had a stern demeanor as he addressed the students during the assembly.
Mr. Maher was quiet, with a stern demeanor and a fondness for racial slurs.
Compare Uncle Sam's stern demeanor to his bizarre outfit, and you'll see what I mean.
The Rev. Hillary Gaston, a 275-pound man with a stern demeanor and a baritone, had been in tense situations before.
"In Greece right now, to be unemployed means death," said Dr. Syrigos, an imposing man with a stern demeanor that grew soft when discussing the plight of cancer patients.
In fact, some of the very same people I had seen drinking on yachts in Venice and being chauffeured around Basel in black-tinted sedans were now affecting a visibly more stern demeanor.
With his stern demeanor, the senator from Massachusetts has the rock-like features of a Thanksgiving pilgrim.
His demeanor remained as stern as ever, and he had a sense of humor that bit more than it tickled, but beneath it was a deep warmth and affection towards me and those he loved that I will always treasure.
To make ends meet, Mr. Allakhverdov, an amateur pianist who was his son's first teacher, still puts aside his slightly stern physician's demeanor and sings in Russian restaurants.
Burns was a police officer before he turned to coaching, and reporters often described his demeanor as that of a beat-walking cop: watchful, stern and disciplined.
I thought she was so stern when I was a kid, but by the time I got to high school, I recognized that her demeanor was rooted in a fight to keep on living.
