Yep, so essentially means the 'basic' definition of immortality or the essence of the word, not the literal meaning of the word.
based on what? Do you have a scan of madara doing so? What will he regenerate from? Immortal, undefeatable, unbeatable, absolute, have been thrown around throughout the entire manga, they are all hyperbole, even edo tenseis were stated to be unkillable, yet they get killed. If Madara's body and chakra are erased, then what does he regenerate from and what powers the regeneration?
ans: nothing.