1
general::
Keen intuition, as in She had a sixth sense that they would find it in the cellar. This term alludes to a sense in addition to the five physical senses of sight, hearing, smell, taste, and touch. [c. 1800]
American Heritage Idioms
2
general::
Phrase(s): a sixth sense
a supposed power to know or feel things that are not perceptible by the five senses of sight, hearing, smell, taste, and touch. • My sixth sense told me to avoid going home by my usual route. Later I discovered there had been a fatal accident on it. • Jane’s sixth sense demanded that she not trust Tom, even though he seemed honest enough.
McGrawhill's American Idioms And Phrasal Verbs