In a manner relating to or characteristic of brilliance; in the way or direction of brightness or excellence.
From 'brilliant' plus the adverbial suffix '-wise,' which creates directional or manner adverbs (like 'likewise,' 'clockwise').
The '-wise' suffix creates adverbs of manner and direction, and 'brilliantwise' is a rare historical example showing how productive this suffix was for creating descriptive terms.
Complete word intelligence in one call. Free tier — 50 lookups/day.