IPA: //ˈsʌbˌruːl//
KK: /sʌbˌruːl/
A specific guideline that explains or clarifies a more general rule.
The subrule provided additional details on how to apply the main regulation.
Subrule → It is formed from "sub-" (meaning under or below) and "rule" (from Latin "regula", meaning a principle or guideline). The word "subrule" refers to a rule that is subordinate or under a main rule.
Think of a rule that is 'under' ('sub-') a main guideline — that's what a subrule means.