second thought vs turnaround

second thought and turnaround both are nouns.

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

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

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

second thought (noun)	turnaround (noun)
thinking again about a choice previously made	turning in the opposite direction
	act or process of unloading and loading and servicing a vessel or aircraft for a return trip
	an area sufficiently large for a vehicle to turn around
	a decision to reverse an earlier decision
	time need to prepare a vessel or ship for a return trip