When a piece of text is difficult to decipher or comprehend, it can be described as "not readable". However, there are a number of alternative terms to convey this message. One option might be to describe the text as "illegible", indicating that it cannot be read or deciphered at all. Alternatively, one might say that the text is "incomprehensible", suggesting that it is difficult to understand or make sense of. Another option might be to use the phrase "unreadable", which carries a similar meaning to "not readable" but may have a slightly different connotation. Ultimately, the choice of synonym will depend on the specific context and audience for whom the text is intended.