1. (

• elusive ,
• subtle

) difficult to detect or grasp by the mind or analyze; "his whole attitude had undergone a subtle change"; "a subtle difference"; "that elusive thing the soul" ;

2. (

• subtle

) able to make fine distinctions; "a subtle mind" ;

3. (

• insidious ,
• pernicious ,
• subtle

) working or spreading in a hidden and usually injurious way; "glaucoma is an insidious disease"; "a subtle poison" ;