Many English adverbs are formed from adjectives by adding the ending "-ly", as in "hopefully", "widely", "theoretically" (for details of spelling and etymology, see "-ly"). Certain words can be used as both adjectives and adverbs, such as "fast", "straight", and "hard"; these are flat adverbs. In earlier usage more flat adverbs were accepted in formal usage; many of these survive in idioms and colloquially. ("That's just plain ugly.") Some adjectives can also be used as flat adverbs when they actually describe the subject. ("The streaker ran naked", not **"The streaker ran nakedly".) The adverb corresponding to the adjective "good" is "well" (note that "bad" forms the regular "badly", although "ill" is occasionally used in some phrases).