IPA: /ˈsɒv.ər.ɪn.li/
KK: /ˈsɑvərɪnli/
In a way that shows complete control or authority; in the highest degree or manner.
The nation acted sovereignly, making decisions without outside interference.
Sovereignly → It is formed from "sovereign" (from Old French *soverain*, meaning supreme ruler or authority) and "-ly" (meaning in a manner of). The word "sovereignly" means in a manner that reflects supreme authority or power.
Think of a supreme ruler ('sovereign') acting in a certain way ('-ly') — that's how you remember that 'sovereignly' means acting with supreme authority.