In «جَنَاحَ الذُّلِّ», the expressed subject is humility, the comparison model is an unspoken bird, and the wing is a distinctive feature of that model.
The mere appearance of the word “wing” does not make the principal metaphor explicit. The modeled creature itself is concealed; therefore the governing metaphor is implicit, and the wing is the feature through which that comparison is imagined.
A common error is to overlook the suppressed model and classify the sentence from a single conspicuous word alone.