• 系けい

  system, lineage, group

• 系図けいず

  family tree, pedigree, genealogy

• 系譜けいふ

  genealogy, lineage, family tree, pedigree

• 系列けいれつ

  series, sequence, system, succession

• 系統けいとう

  system

• 理系りけい

  the sciences, STEM (science, technology, engineering and mathematics)

• 体系たいけい

  system, organization, organisation, architecture

• 日系にっけい

  (of) Japanese descent

• 山系さんけい

  mountain range, mountain system

• 水系すいけい

  water system, river system, drainage system

• 文系ぶんけい

  humanities, social sciences, and fine arts, liberal arts

• 直系ちょっけい

  direct descent, direct line

• 家系かけい

  family lineage

• 生態系せいたいけい

  ecosystem

• 太陽系たいようけい

  solar system

• ＠系アットけい

  roguelike (subgenre of role-playing video games)

• 同系どうけい

  affiliated, akin

• 純系じゅんけい

  pure line, pure strain

• 一系いっけい

  single-family lineage

• 河系かけい

  river system

• 群系ぐんけい

  formation, classification of plant communities

• 医系いけい

  medical, related to medical sciences

• 雲系うんけい

  cloud system

• 世系せいけい

  descent, lineage, bloodline

• 母系ぼけい

  maternal line, mother's side of the family

• Ｖ系ブイけい

  fashion style heavy on make-up and elaborate hairstyles, used among Japanese rock bands, musicians, etc.

• 区系くけい

  ecozone (biogeographical realm)

• 正系せいけい

  legitimate line, direct descent

• Ａ系エーけい

  Akihabara style, nerdy

• 女系じょけい

  female line, matrilinear

• 大系たいけい

  outline, survey, compendium

• 星系せいけい

  star system

• Ｂ系ビーけい

  hip-hop culture, Black culture (esp. breakdancing culture)

• 男系だんけい

  male lineage

• 傍系ぼうけい

  collateral family, subsidiary line, affiliate

• 父系ふけい

  paternal line, father's side of the family

• 系統的けいとうてき

  systematic

• 系統群けいとうぐん

  clade, family

• 系統学けいとうがく

  phylogenetics

• 系譜学けいふがく

  (study of) genealogy

• 系図学けいずがく

  (study of) genealogy

• 系列化けいれつか

  putting in order, systemize, systemise

• 系列的けいれつてき

  paradigmatic, prototypical, representative

• 系統樹けいとうじゅ

  phylogenetic tree, genealogical tree, family tree, evolutionary tree, dendrogram

• 点火系てんかけい

  ignition system

• 体系的たいけいてき

  systematic

• 循環系じゅんかんけい

  circulatory system (blood, lymph, etc.)

• 家系図かけいず

  family tree

• 体系化たいけいか

  systematization, systematisation, organization, organisation

• 共産系きょうさんけい

  communist controlled