IPA: /ˈstɜːr.lɪŋ.li/
KK: /ˈstɜr.lɪŋ.li/
In a way that is excellent or of high quality.
The team performed sterlingly in the championship, impressing everyone with their skills.
Sterlingly is derived from "sterling" (from Old English *styrling*, meaning of high quality or excellent) and the suffix "-ly" (meaning in a manner). The word "sterlingly" means in a manner that is of high quality or excellence.
Think of 'sterling' as representing something of high quality, and remember that 'sterlingly' means doing something in a high-quality manner.