subtle subtle /ˈsʌtəl/

adjective

1. () Difficult to detect or grasp by the mind or analyze  ( elusive , subtle )
   difficult to detect or grasp by the mind or analyze
    His whole attitude had undergone a subtle change
   his whole attitude had undergone a subtle change
    A subtle difference
   a subtle difference
    That elusive thing the soul
   that elusive thing the soul
   
2. Working or spreading in a hidden and usually injurious way  ( insidious , pernicious , subtle )
   working or spreading in a hidden and usually injurious way
    Glaucoma is an insidious disease
   glaucoma is an insidious disease
    A subtle poison
   a subtle poison
   
3. Able to make fine distinctions  ( subtle )
   able to make fine distinctions
    A subtle mind
   a subtle mind