How to say "invalid" in Japanese

• 無効むこうJLPT N1approx.Common
  no-adjective, na-adjectiveCovers the adjective sense: not valid or legally effective, as in a void ticket, contract, or password. This is the word you want whenever 'invalid' means lacking validity, not referring to a person's health.
  脅迫きょうはくのもとになされた約束やくそくは無効むこうだ。↗

  A promise given under a threat is worthless.
• 病人びょうにんCommon
  nounCovers the noun sense of 'invalid' as a sick or chronically ill person. It literally means 'sick person' or 'patient', so for a person, this is the natural choice; it is not used for the 'not valid' sense.
  その看護婦かんごふは病人びょうにんの世話せわをした。↗

  The nurse attended the patient.

Use 無効 for the legal/logical sense of 'invalid' (not valid, void); use 病人 for the noun sense, a sick person, though it literally means 'sick person' rather than 'invalid' as such.

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

• 無効むこうinvalid
• 病人びょうにんsick person
• インバリッドinvalid
• 廃人はいじんcripple
• 病者びょうしゃsick person
• 病弱者びょうじゃくしゃsickly person