IPA: /ʌnˈbrift/
KK: /ʌnˈbrift/
Not having received information or instructions about something.
The team was unbriefed before the meeting, so they were unsure of the agenda.
Unbriefed → It is formed from "un-" (meaning not) and "brief" (from Old French *briefer*, meaning to inform or summarize) and the suffix "-ed" (indicating a past participle). The word "unbriefed" means not having been informed or summarized.
Think of 'not' ('un-') having received a 'summary' or 'information' ('brief') — that's why unbriefed means not informed.