Mirthless
/ˈmɜːrθləs/
Definition 1 of 1
Pro Tip 1/3Sorrowful Expressions
Used to describe facial expressions or laughter lacking genuine amusement. 
Despite the comedian's efforts, the audience's response was a mirthless chuckle.
Pro Tip 2/3Underlying Sadness
The term often implies deeper sadness or discomfort behind the lack of joy. 
His mirthless smile revealed the struggles he faced at home.
Pro Tip 3/3Cultural Nuance
Understanding local behavior is crucial; smiles may differ in meaning across cultures. 
She offered a mirthless nod, not accustomed to the overt cheeriness of her new colleagues.