unfathomable

US /ʌnˈfæð.ə.mə.bəl/
UK /ʌnˈfæð.ə.mə.bəl/
"unfathomable" picture
1.

insondable, incompréhensible, impénétrable

incapable of being fully explored or understood

:
The depths of the ocean are still largely unfathomable.
Les profondeurs de l'océan sont encore largement insondables.
His decision to leave was unfathomable to his family.
Sa décision de partir était incompréhensible pour sa famille.