fundament
n.
late 13c., "foundation, base; buttocks, anus," from Old French fondement "foundation, bottom; land, estate; anus" (12c.), from Latin fundamentum "a foundation, ground-work; support; beginning," from fundare "to found" (see bottom, n.). So called because it is where one sits.
〔蒋〕[fund基础,-a-,-ment名词后缀] 基础,基本原理