体系
たいけい · taikei · JLPT N2 · noun
system
体 (whole body) + 系 (connected line) = parts linked into one whole
体 means body or whole form, and 系 means a connected line or lineage. Together they mean a whole built from linked parts, which is a system.
系 — silk radical 糸 with a stroke on top
Originally a pictograph of a hand holding silk threads, showing connection or lineage. The character depicts threads being tied together, which gave rise to meanings like 'system,' 'lineage,' and 'to connect.' It later became used for organized sequences or relationships.