subtle

Concise Oxford English Dictionary © 2008 Oxford University Press:
subtle /ˈsʌt(ə)l/

▶adjective (subtler, subtlest)

• 1 so delicate or precise as to be difficult to analyse or describe: a subtle distinction.

  ■ capable of making fine distinctions.

  ■ delicately complex and understated: subtle lighting.

• 2 making use of clever and indirect methods to achieve something.

• 3 archaic crafty; cunning.

– derivatives
subtleness noun,
subtlety noun (pl. subtleties),
subtly adverb.

– origin ME: from OFr. sotil, from L. subtilis.