IPA: /ɡrænˈdiːəsli/
KK: /ˈɡrændioʊsli/
In a way that is impressive and extravagant, often to an exaggerated degree.
The event was planned grandiosely, with elaborate decorations and a lavish banquet.
Grandiosely → It is formed from "grand" (from Latin "grandis", meaning large or great) and "-ose" (meaning full of) combined with the adverbial suffix "-ly" (meaning in a manner). The word "grandiosely" means in a manner that is full of grandeur or greatness.
Think of something that is 'large' or 'great' ('grand') and done 'in a manner' ('-ly') that emphasizes its magnificence.
No commonly confused words.