Definitions
1.adjectiveHard to grasp; not obvious or easily understood; barely noticeable."The difference is subtle, but you can hear it if you listen carefully."
2.adjective(of a thing) Cleverly contrived.
3.adjective(of a person or animal) Cunning, skillful.
4.adjectiveInsidious.
5.adjectiveTenuous; rarefied; of low density or thin consistency.
6.adjectiveRefined; exquisite.