系|けいkei[1]atamadaka (head-high)

1. noun, noun (suffix)system; lineage; group
   Windows系けいＯＳではアドミニストレーターアカウントがルートに相当そうとうする。↗

   With Windows OS systems 'administrator account' corresponds to 'root'.
2. noun, mathcorollary
3. noun, noun (suffix), geologysystem (range of strata that correspond to a particular time period)
4. noun, noun (suffix)(taxonomical) series
5. noun (suffix)-type; -ish

• Synonym系列けいれつNeutralRefers to a series or a group of affiliated companies, as in 「系列会社」; stresses members belonging under one system.
• Synonym体系たいけいWrittenWritten/formal prose. Theory or knowledge organized into a whole, as in 「法体系」; stresses the organized whole.
• Synonym系統けいとうNeutralA system or lineage, as in 「消化器系統」「同じ系統の色」; used on its own much more often than 「系」.
• SynonymシステムNeutralLoanword for a system or scheme, as in 「システム開発」; stresses the working of a mechanism.
• Synonym組織そしきNeutralAn organization or group, as in 「組織を作る」; stresses a group of people.
• Related仕組みしくみCasualA mechanism or the way something works, as in 「仕組みを理解する」; common in speech.
• Related構造こうぞうNeutralStructure or construction, as in 「建物の構造」; stresses how parts are put together.
• Related体制たいせいWrittenWritten/formal prose. A political or social system, as in 「政治体制」; stresses the established social order.
• Related編成へんせいWrittenWritten/formal prose. Organizing or arranging things into a unit, as in 「予算編成」; stresses how things are arranged.
• Related構成こうせいNeutralComposition or makeup, as in 「家族構成」; stresses the combination of elements.
• Related組み立てくみたてNeutralAssembly or framework, as in 「文章の組み立て」; stresses how something is built up.
• Related血統けっとうWrittenWritten/formal prose. Bloodline or pedigree, as in 「血統書」; leans toward animals and family descent.
• Related家柄いえがらNeutralFamily background or standing, as in 「家柄がいい」; stresses the family's social rank.
• Related血筋ちすじCasualBloodline or descent, as in 「血筋を引く」; stresses heredity; colloquial.
• Related家筋いえすじCasualA family line handed down through generations; few examples in use. 「家柄」 instead stresses family standing.
• RelatedルーツCasualLoanword for one's roots or origins, as in 「日本人のルーツ」; colloquial.

「系」 usually works as a suffix for a related group or system, as in 「理系」「太陽系」「アニメ系」. On its own, say 「系統」 or 「体系」; for bloodlines use 「血統」, and for how a mechanism works use 「仕組み」. The other words cover structures, organizations and family lines in their own ways.

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

1. （けい） 何なんらかの関係かんけいを持もってつながる、一ひとつのまとまり。
2. （けい） ある定理ていりから容易よういに導き出みちびきだされる命題めいだいで、特とくに言及げんきゅうする必要性ひつようせいがある場合ばあいに焦点しょうてんが当あてられるもの。
3. （けい）対象たいしょうとする範囲はんい。ある関心かんしんによって区切くぎられた世界せかいの特定とくていの部分ぶぶん。
4. （けい）何なんらかの特徴とくちょうや性質せいしつなどをもつ人ひとや集団しゅうだん。