Origin: Germanic Old English suffix
Afterthought has 5 different meanings across 1 category:
thinking again about a choice previously made
"he had second thoughts about his purchase"
an addition that was not included in the original plan
"the garage was an afterthought"
A reflection after an act; a later or subsequent thought, action, or expedient.
To expound as an afterthought.
simple past tense and past participle of afterthink