Definition from Wiktionary, the free dictionary
- 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 book
- (that cannot be read or is not easy to read): illegible, indecipherable, unclear, undecipherable
- (not sufficiently interesting to be worth reading): boring, dull, tedious
Derived terms 
that cannot be read or is not easy to read