An abbreviation or shortened form, possibly for diocese.
From Medieval Latin 'diocesis' (administrative division, from Greek 'diokesis' meaning administration), commonly abbreviated in documents.
Medieval scribes were obsessed with abbreviations to save expensive parchment—they'd use 'dioc' for diocese just like we text 'u' for 'you'—and some of these medieval shortcuts actually survived into modern abbreviations like 'etc.' and 'etc.'
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