an idea, thought, or plan that was not originally intended but is thought of at a later time

She only asked me to her party as an afterthought. 她原本没有请我去参加她的聚会，只是后来才想起来的。

The pillars seem to have been added to the entrance as an afterthought. 这些柱子好像是完工后在入口处添加上去的。