1/2dc adjectives add ē to the stem.
3dc adjectives add ter to the stem, but removing duplicate t

prudens, prudentis → prudent-ter → prudenter
fortis, forte → fortiter (note the stem is forti because all 3dc adjectives are i-stem! (except 1-termination))

some 1/2dc adjectives have an additional -iter ending
durē, duriter

also used as adverb:

  • NT acc SG of adj
    • why accusative instead of nominative?
  • NT abl SG
  • FM abl SG

also a bunch of other ways to form adverbs and also adverbs that don't come from adjectives, like nōn

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