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-on, -ón Augmentative suffix akin to "large."

From Vulgar Latin *-one 'id.' Of unknown origin. It is phonologically possible that it comes from Latin -onem, the accusative of -o, a suffix forming masculine nouns, however this is semantically difficult. If from Latin -o, then from Proto-Italic *-ōn- 'id.' From Proto-Indo-European *h3onh2- 'id.'

Romance: Western Vulgar Latin: Portuguese -ão