You meant "thorough", and you seem to be fixated on the word as it relates to the word "brief". "Brief", the adjective, means "short", basically. The verb seems to be a run-of-the-mill example of verbing a noun, from the word for a lawyer's summary.
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You meant "thorough", and you seem to be fixated on the word as it relates to the word "brief". "Brief", the adjective, means "short", basically. The verb seems to be a run-of-the-mill example of verbing a noun, from the word for a lawyer's summary. The verb does not seem to be very old. The first citation in the OED is from 1861.
verb: give essential information to someone ("The reporters were briefed about the President's plan to invade")
[Wordnet]