底辺|ていへんteihen[1]atamadaka (head-high)

1. noun, geometrybase (of a polygon)
2. nounbottom (of the social scale); lower levels; lower classes
3. nounbase (e.g. of support); foundation; basis
   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.

• Synonym基底きていWrittenWritten word for a foundation or basis; also the mathematical term 'basis'. It lacks 「底辺」's sense of the bottom of society.
• Related基部きぶWrittenWritten, technical word for the base part of an object, the section that connects to its root or foundation.
• Related底そこNeutralThe everyday word for the bottom of things, as in 「鍋の底」; it is not tied to a geometric edge.
• Related麓ふもとNeutralThe foot of a mountain, stressing the low ground at its base; it never means the bottom of society.
• Related底面ていめんNeutralThe base face of a solid; a geometry term. 「底辺」 is the base edge of a flat figure and also means the bottom of society.
• Related底部ていぶWrittenWritten word for the bottom part of an object, with the nuance of its lowest section.
• Related根元ねもとNeutralThe root part of a plant, tree or pillar; by extension, the root or source of a problem.
• Related下様しもざまWrittenArchaic written word for the common people or lower classes; rarely seen today.
• Antonym頂点ちょうてんNeutralThe vertex of a figure or the top of a profession; the direct opposite of 「底辺」 as a base edge.
• Antonym上層じょうそうWrittenThe upper stratum of society or the upper part of a layered whole, as in 「上層部」; the opposite of 「底辺」 in its lower-classes sense.
• AntonymてっぺんCasualColloquial word for the very top of something, as in 「山のてっぺん」; the opposite of a bottom such as 「底」.
• Antonym最高位さいこういWrittenThe highest rank or position; the opposite of 「底辺」 in its social-hierarchy sense.

Use 「底辺」 for the base edge of a flat figure or the bottom of society, as in 「三角形の底辺」 and 「社会の底辺」. For the base face of a solid say 「底面」, for an everyday bottom 「底」, and for the foot of a mountain 「麓」. 「基底」, 「基部」 and 「底部」 are written-style words for foundations and bottoms. The main opposites are 「頂点」 and 「上層」.

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

1. 三角形さんかっけいの頂点ちょうてんに対たいする下したの辺へん。四よん角形かくけいの高たかさに対たいする辺へん。
2. 社会しゃかいの下層かそう。社会的しゃかいてき地位ちいの低ひくい人ひとたち。