IPA: /ʌnˈriːdəbl/
KK: /ʌnˈriːdəbl/
Something that cannot be read or understood easily, often because it is unclear or poorly written.
The author's handwriting was so messy that it was completely unreadable.
Unreadable → It is formed from "un-" (meaning not) and "readable" (from the root "read" which comes from Old English "rǣdan", meaning to interpret or to advise, combined with the suffix "-able" meaning capable of). The word "unreadable" means not capable of being read or interpreted.
Think of 'not' ('un-') being added to 'capable of being read' ('readable') — that's why unreadable means something that cannot be read.