基本

basic / fundamental / main / elementary

(bound form) base; foundation / (bound form) radical (chemistry) / (bound form) gay (loanword from English into Cantonese, Jyutping: gei1, followed by orthographic borrowing from Cantonese)

root / stem / origin / source / this / the current / original / inherent / originally / classifier for books, periodicals, files etc

basically / on the whole

basic skills / fundamentals

fundamental theorem of algebra (every polynomial has a complex root)

the Four Cardinal Principles enunciated by Deng Xiaoping 鄧小平|邓小平[Deng4 Xiao3 ping2] in 1979: to uphold the socialist road, the dictatorship of the proletariat, the leadership of the CCP, and Maoism and Marxism-Leninism

base rate (e.g. interest rate set by central bank)

fundamental doctrine / guiding principle / raison d'être

fundamental principle

basic unit / fundamental building block

fundamental civil rights

fundamental theorem of algebra