undecipherable

verb (used with object)

1. to make out the meaning of (poor or partially obliterated writing, etc.): to decipher a hastily scribbled note.
2. to discover the meaning of (anything obscure or difficult to trace or understand): to decipher hieroglyphics.
3. to interpret by the use of a key, as something written in cipher: to decipher a secret message.
4. Obsolete. to depict; portray.

verb (tr)

1. to determine the meaning of (something obscure or illegible)
2. to convert from code into plain text; decode

adj.1758, from un- (1) “not” + decipherable (see decipher). v.1520s, from de- + cipher. Perhaps in part a loan-translation from Middle French déchiffrer. Related: Deciphered; deciphering.