基礎|きそkiso[1]atamadaka (head-high)

1. no-adjectivefoundation; basis
   その考かんがえが彼かれの理論りろんの基礎きそとなっている。↗

   The idea underlies his theory.

• Synonym土台どだいNeutralA building's foundation or the underpinning of something, as in 「土台を築く」; also an adverb, 'fundamentally', as in 「土台無理だ」. A bit more colloquial than 「基礎」.
• SynonymベースNeutralLoanword for a base, underlying stock or basic tone, as in 「スープのベース」; also a military base or a baseball base. Common in speech; 「基礎」 is the more standard word.
• Synonym基盤きばんNeutralThe conditions that let something stand, as in 「生活基盤」「経営基盤」; mostly for social and economic underpinnings, while 「基礎」 leans to buildings and learning.
• Synonym礎いしずえWrittenWritten and elegant: a cornerstone, or figuratively a person or thing that lays a foundation, as in 「国の礎を築く」. Solemn in tone; in daily speech use 「基礎」.
• Synonym基底きていWrittenWritten term for the underlying base of something or the bottom face of a solid; also the mathematical 'basis'. In daily use 「基礎」 is the normal word.
• Synonym下地したじNeutralPreparatory grounding or aptitude built up in advance, as in 「下地がある」; also an undercoat of paint. Stresses preparation laid down beforehand.
• Synonym基本きほんNeutralThe essentials or core one must grasp, as in 「基本を学ぶ」「基本方針」; 「基礎」 stresses what is laid down to support what rises above.
• Synonym元もとNeutralAn origin, cause or root, as in 「元を正す」「失敗の元」; very common in daily speech, stressing the source, while 「基礎」 stresses what is laid underneath.
• Synonym根底こんていWrittenThe deepest root of something, as in 「根底から覆す」; stresses the depths and leans written, while 「基礎」 is the everyday word.
• Related根っこねっこCasualColloquial for a plant's roots, also figuratively for the essence of a problem, as in 「問題の根っこ」; homely in feel, not used for foundations of learning or buildings.
• Related礎石そせきWrittenWritten word for the stone under a pillar, also figuratively for the foundation of an undertaking, as in 「平和の礎石」; more solemn than 「基礎」 and rare in daily use.
• Related根拠こんきょNeutralThe grounds or reasons backing an argument or judgement, as in 「根拠がない」; about justification, whereas 「基礎」 is about the part laid down underneath.
• Related根ねNeutralLiterally a plant's root, figuratively the source of something, as in 「悪の根」; stresses the origin and does not mean the foundation of learning or a building.
• Related根源こんげんNeutralThe root cause from which something arises, as in 「諸悪の根源」; points to the causal source, while 「基礎」 points to what supports what sits above.
• Related基部きぶWrittenWritten term for the base of an object, as in 「柱の基部」; only a physical part, never an abstract foundation such as that of learning.
• Related根元ねもとNeutralThe part of a tree or post near the ground, as in 「木の根元」, or the root of a problem; points to a physical spot and never to the foundations of learning.
• Related基本原理きほんげんりWrittenWritten term for the most basic, unchanging principles of a field, mostly in academic explanation; narrower than 「基礎」, confined to the level of principles.
• Related根本原理こんぽんげんりFormalFormal term for the most fundamental principles or laws, mostly in discourse; close to 「基本原理」 and even more confined to principles than 「基礎」.
• Antonym応用おうようNeutralAntonym: putting theory or knowledge to practical use, as in 「応用問題」; stands opposite to the groundwork stage that 「基礎」 names.

Use 「基礎」 for a building's foundation or the groundwork of learning, as in 「基礎知識」. Pick 「基本」 for the essential points, 「基盤」 for social or economic underpinnings, 「根拠」 for grounds or evidence, 「根源」 for the source of something; 「応用」 is the opposite. 土台 and ベース are looser, speechier stand-ins; 礎, 礎石 and 根底 are solemn written words; 根元, 根っこ, 根 and 基部 name physical roots or bases; 元 is the everyday word for an origin or cause; 下地 is preparation laid in advance; 基本原理 and 根本原理 stay at the level of principles.

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

1. 建物たてものを支持しじし、その重量じゅうりょうを安全あんぜんに地盤じばんに伝つたえるために、建物たてものの下部かぶに作つくられた土台どだいの総称そうしょう。
2. 物事ものごとを成立せいりつさせるのに必須ひっすの事柄ことがら。