وَالْكَلَامُ مِثْلُ كَلَامٍ فَصِيحٍ وَقَصِيدَةٍ فَصِيحَةٍ
Discourse too is described as fasih, as in fasih speech and a fasih poem.
Unlike an isolated word, discourse combines words. Its evaluation must consider how their arrangement affects sound and intelligibility. Even when individual words are acceptable, their combination may create a difficulty.
Thus, calling discourse fasih is more than declaring that each constituent word is individually fasih; it also evaluates the arrangement of those words.