The present participle of fellow; the act of uniting with, treating as, or acknowledging someone as a fellow or equal.
From the verb 'fellow' with the present participle suffix '-ing,' creating the continuous or gerund form. This allows the action of treating someone as an equal to be described as an ongoing process.
The fact that 'fellowing' is grammatically correct but almost never used shows that English is full of technically valid words that people just stopped using—they're like extinct paths in the forest of language!
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