How to say "unofficial" in Japanese

• 非公式ひこうしきCommon
  no-adjective, na-adjectiveCovers the neutral sense of 'unofficial': something done, said or arranged without official status or formality. This is the word you want for ordinary unofficial matters, as opposed to anything shady or illegal.
  ウーマン・リブは底辺ていへんは広ひろいが、非公式ひこうしきな民衆みんしゅうの運動うんどうである。↗

  Women's Liberation is a broad-based but informal popular movement.
• アングラCommon
  prenominal modifierAn abbreviation of 'underground'; it really covers the clandestine side — the underground economy or press, illegal dealings, black money. For merely unofficial matters it is seldom the word you want.

Use 非公式 for the plain sense of 'unofficial', something not official or informal; 「アングラ」, an abbreviation of 'underground', fits the underground or illegal sense, as in the underground economy.

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

• 非公式ひこうしきinformal
• 非公認ひこうにんunofficial
• 私製しせいprivately-made (esp. postcard, mailing card, etc.)
• アングラunderground (economy, press, etc.)
• アンダーグラウンドunderground (economy, press, etc.)
• 勝手かってunauthorised (e.g. phone app, WWW site)