There are two additional means to gather adverbial force from an active adjective within a sentence: (a) with a neuter accusative and (b) with a ablative neuter or feminine singular.
The neuter accusative of nouns.
- He thinks a great deal of you: tibi multum probat.
- She will accomplish it easily: id facile perficēbit. (note, facile, with id, not facilē)
- What are you doing: quem facis?
- Why are you doing that: quid istud facis?
The ablative neuter or plural.
- This option generally has some noun implied.
- She spoke falsely: ea falsō (verbō) locūta est.
- Let us continue straight: rectā (viā) permaneāmus.
- Rain fails frequently: imber crebrō (tempore) cadit.
- She is commonly known as the Witch: Malefica volgā (famā) nōtā est.
The Essential AG: 214d-e