afterthought
1. [ noun ] (psychology) thinking again about a choice previously made
Synonyms: second_thought rethink reconsideration
Examples:

"he had second thoughts about his purchase"

Related terms: reversal rethink
2. [ noun ] an addition that was not included in the original plan
Examples:

"the garage was an afterthought"

Related terms: addition
Similar spelling:   afterbirth
  aftermath
  aftermost
  after_part
  aftertaste
  after-hours
  after_hours
  after-school