comparative-greater
superlative-greatest
most brilliant
Consider the adjective "bright." The comparative form is brighter, the superlative form is brightest.
Adjectives can be classified by degree. If the positive form is bright, the comparative form is brighter and the superlative form is brightest.
The usual adverb form is brightly. Rarely, bright itself is used as an adverb (The fire burning bright).Reflecting this, the comparative and superlative forms are sometimes the same as the adjective: brighter (more brightly) or brightest (most brightly).
bright, brighter, brightest
The comparative form of busy is busier.
The comparative form of friendly is friendlier.
The comparative form of dreamy is dreamier
comparative form is cleaner superlative form is cleanest
The comparative form of many is more
The comparative form of "central" is "more central."
Comparative and Superlative forms are for Adjectives and brightly is an Adverb, therefore there is no comparative or superlative for brightly. The forms brighter and brightest exist as the comparative and superaltive forms of the adjective bright.