different between unreadable vs readability

English

un- +? readable

unreadable (comparative more unreadable, superlative most unreadable)

That cannot be read or is not easy to read.
unreadable handwriting
a machine that cut up secret documents into small unreadable fragments
unreadable charts
Not sufficiently interesting to be worth reading.
unreadable books

(that cannot be read or is not easy to read): illegible, indecipherable, unclear, undecipherable
(not sufficiently interesting to be worth reading): boring, dull, tedious

readable +? -ity.

readability (countable and uncountable, plural readabilities)

The property of being capable of being read; legibility.
The property of being easy or engaging to read.
The book had a clever plot, but lacked readability.

Send