In a greeting manner; with a greeting; in a way that greets or welcomes.
From 'greeting' (gerund of 'greet') plus the adverbial suffix '-ly.' The construction 'greeting' + '-ly' creates an adverb meaning 'in a greeting-like manner.'
The '-ly' suffix is endlessly flexible—'greetingly' isn't common but it's perfectly intelligible because English speakers understand the pattern instantly: we can add '-ly' to almost any word!
Complete word intelligence in one call. Free tier — 50 lookups/day.