How to say "default" in Japanese

• 不履行ふりこうCommon
  nounThe general term for failure to perform an obligation, i.e. 'default' in its legal sense; it covers nonperformance of duties under a contract or loan.
• 不払いふばらいCommon
  nounNonpayment — money owed but not paid. Use this when 'default' means simply that a payment was not made, rather than a broader failure to perform.
• 違約いやくCommon
  noun, suru verb, intransitive verbPrimarily 'breach of contract': violating the terms of an agreement. It fits 'default' only when the failure amounts to such a breach; for plain nonpayment it is not the word you want.
• 滞納たいのうJLPT N1approx.Common
  noun, suru verb, transitive verbFalling behind with payments: being in arrears. It treats default as an ongoing state of money owed and unpaid, as with rent or taxes allowed to pile up.
  数すう日じつならまだしも１０日にちも滞納たいのうしている。↗

  A few days would have been excusable, but you are in arrears for 10 days.

For default as failure to perform an obligation use 不履行; for simple nonpayment 「不払い」; 違約 only when a contract is breached; 滞納 for falling behind on payments, i.e. being in arrears.

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

• 不履行ふりこうdefault
• 不払いふばらいnonpayment
• 違約いやくbreach of contract
• 滞納たいのうfalling behind (with a payment)
• デフォルトdefault
• デフォdefault
• 省略時しょうりゃくじdefault
• 不納ふのうnon-payment
• 黙約もくやくtacit agreement
• 不戦敗ふせんぱいloss by default