Definition from Wiktionary, the free dictionary
afterthought (plural afterthoughts)
- A reflection after an act; a later or subsequent thought, action, or expedient.
- She packed her sandals only as an afterthought, but she was glad she did.
- Something additional to the original plan or concept.
- This whole remodeling was an afterthought, we were only going to paint and call it good.
a subsequent thought
- (very rare except in the past tense, possibly nonstandard) To expound as an afterthought.