Her dance moves flow with such effortlessness that it looks completely natural.

effortlessness 是由名词 effort（努力）加上后缀 -less（表示“没有”）构成形容词 effortless（不费力的），再加上名词后缀 -ness 构成的名词，表示“轻松自如、毫不费力”的状态。