平ら|たいらtaira[0]heiban (flat)

1. na-adjectiveflat; level; even; smooth
   あの山やまの頂上ちょうじょうは平たいらだ。↗

   The top of that mountain is flat.
2. na-adjectivecalm; tranquil; placid; composed; stable
3. na-adjectiverelaxed (sitting posture); comfortableusu. as お平らに
4. noun (suffix)plateau; tableland; plainafter a place name, usu. だいら

• Synonym水平すいへいNeutralMeans horizontal or level, as in 「水平な線」; judged against the horizontal plane, i.e. not tilted.
• Synonym平たいひらたいNeutralMeans flat and thin, or plain and easy to follow in wording, as in 「平たく言えば」.
• Synonym平坦へいたんNeutralFor flat ground, and by extension a life or path with no obstacles, as in 「平坦な道」; leans slightly toward written style.
• SynonymフラットNeutralLoanword for flat or level, also the musical flat (♭) and exact round amounts, as in 「10秒フラット」.
• Synonym平らかたいらかWrittenWritten-style word for flat terrain or a peaceful, settled state; rare in modern Japanese.
• Synonym平滑へいかつWrittenWritten word meaning flat and smooth; often used in technical descriptions of surfaces.
• Synonym平ったいひらったいCasualColloquial variant of 「平たい」, meaning flat or flattened.
• Related滑らかなめらかNeutralMeans smooth, as in 「滑らかな肌」; it is about texture or flow rather than the absence of highs and lows.
• Related平面的へいめんてきWrittenWritten word for flat in the sense of lacking depth or a third dimension; figuratively, superficial or one-dimensional.
• RelatedなだらかNeutralDescribes a gentle slope, as in 「なだらかな丘」; not completely flat, just gradually rising or falling.
• Antonym凸凹でこぼこNeutralAntonym of 「平ら」: uneven or bumpy, with a surface rising and dipping.
• Antonym起伏きふくNeutralAntonym of 「平ら」: undulation, whether of terrain or of emotions, with highs and lows.

Use 「平ら」 for a surface with no highs or lows. For flat ground say 「平坦」, for something flat and thin 「平たい」, for smooth texture 「滑らか」, for a gentle slope 「なだらか」, and for not tilted 「水平」. 「凸凹」 and 「起伏」 are opposites. 「平らか」 and 「平滑」 are written style, 「平ったい」 colloquial, 「平面的」 about flatness lacking depth, and 「フラット」 a loanword also covering the musical flat and exact amounts.

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

1. 高低こうていや凹凸おうとつのないさま。
2. 心こころや政情せいじょうなどが安定あんていしているさま。
3. 楽らくな姿勢しせいをとるさま。