Meaning hard, harsh, or severe in manner or character:
The teacher looked at the misbehaving student sternly before addressing the class.
I can give you several sentences.He spoke sternly to the misbehaving students.I backed down when he glared sternly at me."Follow your orders," the sergeant said sternly.
If it's a meaning you want, 'sternly' means 'harshly' or 'firmly'.
Example sentence - His father spoke sternly to him when he behaved badly.
Firm or unyielding, uncompromising.
"Sternly" means to do something in a serious, strict, or harsh manner. It often conveys a sense of authority or firmness, typically used when addressing behavior that is undesirable or unacceptable. For example, a parent might speak sternly to a child to emphasize the importance of following rules.
They are synonyms, not antonyms.
Reprimanded
Lamented or sternly
Sternly disciplined, brave, undaunted
it means with sternness; in a severe manner.
grimly, sternly, austerely, seriously, solemnly, thoughtfully