Ḍāfin describes something long, abundant, and flowing; here it concerns the horse’s full tail. Fuwayqa al-arḍ is a diminutive form of fawqa, meaning “just a little above the ground.”
Laysa bi-aʿzal denies that the tail is sparse or lacking hair on one side. The ideal is not merely length but fullness, symmetry, and a suitable distance from the ground.
The diminutive fuwayqa gives a fine measurement of proximity: the tail hangs low, but does not drag.