Impossible to decipher: indecipherable handwriting; an indecipherable message. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "indecipherable" in a sentence
"The characters are empty stereotypes, who often behave in indecipherable ways, and the dialogue is so awful it made me laugh out loud at least four or five times."
"(Sorry Tommy, an increase in indecipherable gibberish doesn’t cut it!)."
"Her expression was indecipherable, her features refusing to relate to each other in a meaningful way."