天然|てんねんtennen[0]heiban (flat)

1. no-adjectivenature; spontaneity
   この車くるまは天然てんねんガスで動うごく。↗

   This car runs on natural gas.
2. no-adjectivenatural airhead

• Synonym自然しぜんNeutralBroader term: covers nature itself and things happening naturally. 「天然」 stresses being formed without human touch, as in 「天然水」.
• Related生まれつきうまれつきNeutralFor innate qualities one is born with; stresses a person's inborn traits, not naturally formed things.
• Related元来がんらいWrittenWritten adverb meaning originally or essentially; stresses what something is like by its original nature.
• Related根っからねっからCasualColloquial: by nature, to the core, as in 「根っからの悪人ではない」.
• Related自然状態しぜんじょうたいWrittenWritten, academic term for a state untouched by human intervention; in everyday speech say 「自然のまま」.
• Related生まれながらうまれながらNeutralFor qualities one has from birth, as in 「生まれながらの才能」; somewhat bookish.
• Related生得せいとくWrittenWritten term for innate, inborn qualities; rare.
• Related根からねからCasualColloquial: by nature, from the root; often used with negatives; rare.
• Antonym人工じんこうNeutralAntonym: artificial or man-made, as in 「人工芝」; the direct opposite of 「天然」.
• Antonym人造じんぞうNeutralAntonym: man-made or imitation, as in 「人造湖」; also contrasts with 「天然」.

Use 「天然」 for things formed without human hands or a natural airhead, as in 「天然水」 and 「天然ボケ」. For nature itself use 「自然」; for innate traits say 「生まれつき」. 「人工」 and 「人造」 are the opposites.

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

1. 人ひとの手ての加くわわっていない自然しぜんのままの状態じょうたい。
2. 生うまれつき持もっているもの。
3. 天然てんねんボケ。