Her slyness was apparent as she cleverly hid her true intentions behind a joke.

slyness 是由形容词 sly（狡猾的、狡黠的）加上名词后缀 -ness 构成的名词，表示"狡猾的特性或状态"。sly 本身源自古英语，有"狡猾、诡计多端"的含义。