The quality of being fervent; intense, passionate, or deeply felt enthusiasm, belief, or emotion.
From Latin 'ferventia' (heat, passion) with the English abstract noun suffix '-cy' added to create a noun form. It parallels the slightly more common variant 'fervence'.
Medieval preachers used 'fervency' to describe the burning intensity of religious faith—the word itself suggests something almost physical, like your passion is actually getting hot enough to boil over.
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