sixth sense vs insight

sixth sense and insight both are nouns.

Word	Noun	Adjective	Verb	Adverb
sixth sense	Yes	No	No	No
insight	Yes	No	No	No

As nouns, sixth sense and insight are synonyms defined as:

sixth sense and insight: grasping the inner nature of things intuitively

sixth sense (noun)	insight (noun)
grasping the inner nature of things intuitively	grasping the inner nature of things intuitively
	the clear (and often sudden) understanding of a complex situation
	clear or deep perception of a situation
	a feeling of understanding