無効な

• Reading: むこうな
• Romaji: mukou na
• Kanji breakdown: 無 (mu) — without, nothing; 効 (kou) — effect, efficacy
• Pronunciation: /mɯ.koː.na/

Meaning

Invalid; void; null; having no legal or practical effect.

A na-adjective describing something that has no validity or legal force. Commonly used for expired tickets (無効なチケット), voided contracts (契約を無効にする), and invalid data in computing contexts. The opposite is 有効な (valid/effective). The noun form 無効 is also frequently used on its own.

Examples

1. このパスワードは無効なので再設定してください。 This password is invalid, so please reset it.
2. 契約書に不備があり無効な状態になっていた。 There were deficiencies in the contract, leaving it in an invalid state.
3. 期限切れの免許証は無効なため運転できない。 An expired driver's license is invalid, so you cannot drive.

Usage Guide

Context: legal, computing, administration, contracts

Tone: matter-of-fact

Origin & History

From Sino-Japanese 無 (mu, without/nothing) + 効 (kou, effect/efficacy) + な (na, adjectival suffix). Literally 'without effect,' describing something that lacks validity or binding power.

Cultural Context

Era: Modern

Generation: Adults

Social background: Universal