IPA: /ˈɡrɪnɪŋli/
KK: /ˈɡrɪnɪŋli/
In a way that shows a smile, often indicating happiness or amusement.
She looked at him grinningly, clearly pleased with the joke.
Grinningly is formed from "grin" (of uncertain origin, possibly related to Old English "grennian", meaning to grin or smile) and the suffix "-ly" (meaning in a manner of). The word describes the manner of smiling or showing teeth in a grin.
Think of someone smiling broadly, as 'grinning' means to smile widely, and '-ly' indicates the manner in which they are doing it.