lineage, system
系 centers on connected lines of descent or organization: a lineage, family line, or a structured system of related parts.
系 combines a top stroke 丿 with 糸 (thread), suggesting a thread that connects or ties together, extended to lineage and systems.
The top stroke 丿 is like a hook or knot, and 糸 is thread. Picture a thread hanging down from a knot, linking generations in a family line or connecting parts of a system.
For ケイ, imagine a long family line stretching like a cable: cable -> ケイ, and the thread of lineage keeps everyone connected.
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system; lineage; group
series; sequence; system; succession
system
system; organization; organisation; architecture
the sciences; STEM (science, technology, engineering and mathematics)
family lineage
(of) Japanese descent
humanities, social sciences, and fine arts; liberal arts
solar system
genealogy; lineage; family tree; pedigree
Milky Way galaxy; Milky Way; the Galaxy
direct descent; direct line
water system; river system; drainage system
female line; matrilinear
affiliated; akin
family tree; pedigree; genealogy
male lineage
mountain range; mountain system
outline; survey; compendium
paternal line; father's side of the family