In a convivial manner; in a way that is friendly, festive, and sociable.
From convivial plus -ly, the standard adverbial suffix. This forms adverbs from adjectives following a pattern unchanged since Old English.
The -ly adverb suffix is so ubiquitous that we barely notice it, but it's actually a reduced form of the Old English word 'lice' (like), which meant 'in the manner of'—so 'convivially' literally means 'in a convivial manner' or 'in a convivial way.'
Complete word intelligence in one call. Free tier — 50 lookups/day.