IPA: /ˌmʌltiˈvɛrɪbəl/
KK: /mʌltɪˈvɛrɪbəl/
Relating to or involving multiple factors or variables at the same time.
In multivariable calculus, we study functions that depend on more than one variable.
Multivariable → It is formed from "multi-" (meaning many) and "variable" (from Latin "variabilis", meaning changeable). The word "multivariable" refers to something that involves many changeable factors or variables.
Think of 'many' ('multi-') factors that can 'change' ('variable') — that's what multivariable means.