His frustration was visibly apparent during the heated discussion.

visibly 是形容词 visible（可见的）加上副词后缀 -ly 构成的副词，表示"明显地、显而易见地"。visible 来自拉丁词根 vis（看、看见），加上形容词后缀 -ible（能够...的），字面意思是"能够被看见的"。