C2 adjective /ˌɪndɪˈfætɪɡəbl̩/
indefatigable
inébranlable
Meaning
persisting tirelessly; incapable of being fatigued
Example
Her indefatigable spirit kept the team motivated during the long project.
Son esprit inébranlable a gardé l'équipe motivée pendant le long projet.