Indecipherable/ˌɪndɪˈsaɪfrəbl/ Definition 1 of 2Pro Tip 1/3Unreadable Writing Used when someone's handwriting is so bad, you can't read it. I tried to read his note, but it was indecipherable. Pro Tip 2/3Complex Jargon When specialized language is used and it's too complex for outsiders to understand. The medical report was indecipherable to anyone not a doctor. Pro Tip 3/3Mystery Languages Refers to the difficulty of understanding unknown or ancient languages. The archaeologists found indecipherable inscriptions on the ruins.