mirth‧less /ˈmɜːθləs $ ˈmɜːrθ-/
adjective literary mirthless laughter or a mirthless smile does not seem to be caused by real amusement or happiness:
‘Now it’s your turn,’ he said with a mirthless grin.—mirthlessly adverb:
He smiled mirthlessly. [TahlilGaran] Dictionary of Contemporary English ▲