Where does “虚数単位” come from?

虚数単位 (Japanese) comes from Japanese 単位, from Middle Chinese 單位.

虚数単位 (Japanese): an imaginary unit

Definitions

  1. an imaginary unit

Ancestry of “虚数単位”, step by step

虚数単位 traces back through two separate lines of ancestry.

via Japanese 単位

StepLanguageWordMeaning
1Japanese単位unit of measure; unit; academic credit
2Middle Chinese單位—

via Japanese 虚数

StepLanguageWordMeaning
1Japanese虚数an imaginary number
Every word from Middle Chinese 單位 →Every word from Japanese 単位 →
虚数単位 — Etymology, Origin & Word History | Etymology Explorer