subtlest

adjective subtler , subtlest

1. thin; rare; tenuous; not dense or heavy: a subtle gas
2. 1. capable of making or noticing fine distinctions in meaning, etc.: a subtle thinker
   2. marked by or requiring mental keenness: subtle reasoning
3. delicately skillful or clever; deft or ingenious: a subtle filigree
4. not open or direct; crafty; sly
5. delicately suggestive; not grossly obvious: a subtle hint
6. working insidiously; not easily detected: a subtle poison