IPA: //ˈflɪərɪŋli//
KK: /ˈflɪrɪŋli/
In a mocking or sneering way, often showing contempt or disdain.
He looked at her fleeringly, making it clear he didn't take her seriously.
Fleeringly → It is formed from "fleer" (from Middle English *fleeren*, meaning to grin or smile in a mocking way) and the adverbial suffix "-ingly" (meaning in a manner of). The word "fleeringly" describes the manner of grinning or smiling in a mocking or derisive way.
Think of someone grinning in a mocking way — that's what 'fleeringly' means, as it comes from 'fleer' which means to mock or grin.