Meaning of subtle

sub•tle

1. thin, tenuous, or rarefied, as a fluid or an odor.
2. fine or delicate in meaning or intent; difficult to perceive or understand: subtle irony.
3. delicate or faint and mysterious: a subtle smile.
4. requiring mental acuteness, penetration, or discernment: a subtle philosophy.
5. characterized by mental acuteness or penetration: a subtle understanding.
6. cunning, wily, or crafty: a subtle liar.
7. insidious in operation: subtle poison.
8. skillful, clever, or ingenious: a subtle painter.