«فتنافر الحروف: وصف في الكلمة يوجب ثقلها على اللسان، وعسر النطق بها»
Sound discord is a quality of a word that burdens the tongue and makes it hard to pronounce.
The issue is how the sounds occur together. A long word may still be smooth, while a shorter consonant sequence can be difficult to articulate.
The relevant standard is Arabic usage and the word's phonetic structure, not merely whether an inexperienced learner finds an unfamiliar word challenging.