How to say "unintelligible" in Japanese

• 難解なんかいCommon
  na-adjective, nounCovers the sense of unintelligible as genuinely abstruse or difficult to understand, implying depth or complexity. Typical of difficult academic writing, theory, or arguments that take real effort to grasp.
  現代詩げんだいしはしばしばきわめて難解なんかいだ。↗

  Modern poetry is often most obscure.
• わかりにくいCommon
  i-adjectiveCovers unintelligible as hard to understand or incomprehensible in an everyday way — something unclear or poorly expressed rather than profound. Usually written in kana alone; a natural default when you simply cannot make something out.

Use 難解 for something intrinsically difficult and abstruse, and 「わかりにくい」 for something that simply fails to come across clearly; the latter is the everyday, kana-written choice.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 難解なんかいdifficult to understand
• わかりにくいhard to understand
• 詰屈きっくつhard to understand