second thought vs reversal

second thought and reversal both are nouns.

Word	Noun	Adjective	Verb	Adverb
second thought	Yes	No	No	No
reversal	Yes	No	No	No

As nouns, reversal is a hypernym of second thought; that is, reversal is a word with a broader meaning than second thought:

Other hypernyms of second thought include change of mind, flip-flop, turnabout, turnaround.

second thought (noun)	reversal (noun)
thinking again about a choice previously made	a change from one state to the opposite state
	the act of reversing the order or place of
	turning in the opposite direction
	a major change in attitude or principle or point of view
	a judgment by a higher court that the judgment of a lower court was incorrect and should be set aside
	a decision to reverse an earlier decision
	turning in an opposite direction or position
	an unfortunate happening that hinders or impedes; something that is thwarting or frustrating