IPA: /ˈθɪnli/
KK: /θɪnli/
In a way that is not thick; in a sparse or scattered manner.
She sliced the vegetables thinly for the salad.
Thinly → It is formed from "thin" (from Old English "þynn", meaning not thick or narrow) and "-ly" (a suffix used to form adverbs). The word "thinly" means in a manner that is not thick or in a narrow way.
Think of something that is 'not thick' ('thin') and how it is done in a way ('-ly'). This helps you remember that 'thinly' means to do something in a way that is not thick.