IPA: /ˈsʌbˌɪntərvəl/
KK: /sʌbˈɪntərvəl/
A smaller section or part of a larger interval, often used in mathematics to describe divisions within a range.
In calculus, we often analyze the properties of a function over a subinterval of its domain.
Subinterval → It is formed from "sub-" (meaning under or below) and "interval" (from Latin "intervallum", meaning a space between). The word "subinterval" refers to a smaller interval that exists within a larger one, hence something that is under or part of a larger space between two points.
Think of a smaller space ('sub-') that exists within a larger space ('interval'). This helps you remember that a subinterval is a part of a larger interval.