afterthought vs turnabout

afterthought and turnabout both are nouns.

Word	Noun	Adjective	Verb	Adverb
afterthought	Yes	No	No	No
turnabout	Yes	No	No	No

As nouns, turnabout is a hypernym of afterthought; that is, turnabout is a word with a broader meaning than afterthought:

Other hypernyms of afterthought include change of mind, flip-flop, reversal, turnaround.

afterthought (noun)	turnabout (noun)
an addition that was not included in the original plan	turning in the opposite direction
thinking again about a choice previously made	a decision to reverse an earlier decision