stern
STURNadjMeaning serious and strict in manner
Memory hook a STERN STARE. Principal Victor gives the noisy hallway one long stare, and everyone falls silent. A serious, strict look like that is stern.
One stern look from the librarian quieted the whole table.
In context Grandpa’s voice was stern when he found the open gate, but he was not cruel; he simply explained why the sheep must never be left loose again.
Similar strict, severe, serious, grim
Opposite gentle, lenient, kindly