平行(へいこう)

へいこう
noun, na-adjective
parallel
science
See also: 並行(へいこう) (parallel, concurrent)
1. parallel
Lines or surfaces that maintain equal distance and never intersect.
この二(ふた)つの線(せん)は平行(へいこう)だ。
These two lines are parallel.
線路(せんろ)は平行(へいこう)に走(はし)っている。
The railroad tracks run parallel to each other.
平行(へいこう)な二(ふた)つの線(せん)はどこまで伸(の)ばしても交(まじ)わらない。
Two parallel lines never intersect no matter how far they are extended.
2. simultaneous; concurrent
Doing multiple things at the same time. In this sense the standard spelling uses a different kanji (see the notes); this one is common but nonstandard in edited writing.
仕事(しごと)と勉強(べんきょう)を平行(へいこう)して進(すす)める。
To pursue work and studies simultaneously.
二(ふた)つのプロジェクトを平行(へいこう)して進(すす)めている。
We are working on two projects simultaneously.
話(はな)し合(あ)いは平行線(へいこうせん)のままで、なかなか結論(けつろん)が出(で)なかった。
The discussion remained at a stalemate, and no conclusion was reached.
平行線(へいこうせん) (parallel lines) is used figuratively to mean that two sides cannot reach agreement.

平行(へいこう) has both a geometric meaning (parallel lines) and a figurative meaning (doing things simultaneously).

Compounds

Usage

平行(へいこう) and 並行(へいこう) are homophones. 平行(へいこう) emphasizes the geometric sense; 並行(へいこう) is preferred for "concurrent" or "alongside."

Related words

Related Words

Homophone: 平衡(へいこう) (balance)
Antonym: 垂直(すいちょく) (perpendicular)
Related: 平行四辺形(へいこうしへんけい) (parallelogram)
general
Added 2026.1.16 16:37 · Revised 2026.10.7 9:40
05000/05445_heikou