Meaning : Difficult to detect or grasp by the mind or analyze.
Example :
His whole attitude had undergone a subtle change.
A subtle difference.
That elusive thing the soul.
Synonyms : elusive
Meaning : Able to make fine distinctions.
Example :
A subtle mind.
Meaning : Working or spreading in a hidden and usually injurious way.
Example :
Glaucoma is an insidious disease.
A subtle poison.
Synonyms : insidious, pernicious