indecipherable

From in- +‎ decipherable.

• IPA^(key): /ɪndɪˈsaɪfəɹəbəl/, /ɪndɪˈsaɪfɹəbəl/, /ɪndə-/

indecipherable (comparative more indecipherable, superlative most indecipherable)

1. Not decipherable; impossible to decode, read, understand or comprehend.

   The doctor's handwriting was indecipherable.

   • 2012 October 8, Daniel W. Patterson, The True Image: Gravestone Art and the Culture of Scotch Irish Settlers in the Pennsylvania and Carolina Backcountry‎, UNC Press Books, →ISBN, page 141:

     The second and third quarters of the shield are indecipherable on the stone but clearer in two other representations of the arms, a painted wooden funeral hatchment for Mary Davie […]

2. Indistinguishable
   • 2001 December 22, Michael A. Norville, “Why do so many DMs hate their players”, in rec.games.frp.dnd‎ (Usenet):

     The explanation some are suggesting is that the object takes on the appearance of what is behind it, or that it takes on the appearanec ^[sic] of what the observer thinks is behind it. In both cases, the object is still visible. It's a visible representation of what's behind it, but it is still invisible, just indecipherable from its surroundings.

   • 2004 April 21, RoyWilliamsIsGay, “Pablo the Troll”, in alt.sports.football.pro.phila-eagles‎ (Usenet):

     If you knew who Jerry was you'd swear you'd been cloned. Your posting style is virtually indecipherable from his.

   • 2015 May 20, Laura Pintur, “My campaign against Zoo Magazine: the well-being of girls should come before profits” (0:25 from the start), in Guardian Australia‎:

     A British university compared lads' mags with comments from convicted rapists. It found that people could not distinguish the source of the comments. That is, Zoo uses language practically indecipherable from that of sex offenders.

• undecipherable
• unreadable
• illegible

• decipherable

• indecipherable, undecipherable at Google Ngram Viewer