وإن تعدد طرفه الثاني دون الأول فتشبيه الجمع
When the second term is multiple but the first is not, it is called a gathering simile.
A single subject is described through several comparison terms. A smile or bright teeth, for instance, may be likened to several luminous or white things. The subject remains one; the reference images are multiple.
This is the converse of taswiya: taswiya = several subjects plus one comparison term, whereas jamʿ = one subject plus several comparison terms. Identify the relationships, not merely the number of nouns in the sentence.