直線|ちょくせんchokusen[0]heiban (flat)

1. no-adjectivestraight line
   この２つの直線ちょくせんは直角ちょっかくに交まじわっている。↗

   These two lines are at right angles.

• Synonym一直線いっちょくせんNeutralA single straight line; often used adverbially for going straight or single-mindedly, as in 「一直線に走る」. Stresses having no bends or turns more strongly than 「直線」.
• Related棒線ぼうせんNeutralA straight line drawn like a rod or stick; mostly in charts, diagrams and annotation marks. For straight lines in general, 「直線」 is the word.
• Antonym曲線きょくせんNeutralA curve, the direct opposite of 「直線」 (cf. 「曲線美」). In mathematics it is also the general term for lines, including straight ones.
• Antonym曲がりまがりNeutralA noun for a bend — a place where something curves, or the degree of bending — set against the straightness of 「直線」.
• Antonym屈曲くっきょくWrittenA formal, written-style word for bending or flexing, opposed to 「直線」; common in medical and anatomical descriptions.

Use 「直線」 for straight lines in mathematics and on roads (「直線距離」). For going straight or single-mindedly, use 「一直線」. The opposites are 「曲線」 and 「曲がり」.

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

1. 無限むげんに真っ直まっすぐ伸のびた線せん。