second thought vs flip-flop

second thought and flip-flop both are nouns.

Word	Noun	Adjective	Verb	Adverb
second thought	Yes	No	No	No
flip-flop	Yes	No	Yes	No

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

Other hypernyms of second thought include change of mind, reversal, turnabout, turnaround.

second thought (noun)	flip-flop (noun)
thinking again about a choice previously made	a backward somersault
	an electronic circuit that can assume either of two stable states
	a backless sandal held to the foot by a thong between the big toe and the second toe
	a decision to reverse an earlier decision

second thought (verb)	flip-flop (verb)
	reverse (a direction, attitude, or course of action)