IPA: /ˈɪntəˌrɛks/
KK: /ɪnˈtɛrˌrɛks/
A person who temporarily rules or governs during a period when there is no official leader, often used in historical contexts.
During the interregnum, the interrex ensured that the government continued to function smoothly until a new leader was elected.
Interrex → It is formed from "inter-" (meaning between) and "rex" (meaning king). The term refers to a temporary ruler who governs in the absence of a king, thus governing 'between' kings.
Think of someone ruling 'between' kings — 'inter-' means between, and 'rex' means king.
No commonly confused words.