In a manner that is irritating, bothersome, or frustrating; in a way that causes annoyance.
From annoying (present participle of annoy, from Old French anoier from Latin in odio 'in hate') + '-ly' (Old English adverbial suffix). The word developed in English by the 16th century.
The word 'annoyingly' is adjectival applied to actions—we say 'annoyingly slowly' or 'annoyingly cheerful'—but this means we're describing how an action makes us feel rather than the action itself, showing how adverbs often carry emotional judgments even when they seem neutral.
Complete word intelligence in one call. Free tier — 50 lookups/day.