adj. sub·tler, sub·tlest
a. So slight as to be difficult to detect or describe; elusive: a subtle smile.
b. Difficult to understand; abstruse: an argument whose subtle point was lost on her opponent.
2. Able to make fine distinctions: a subtle mind.
3. Operating in a hidden, usually injurious way; insidious: a subtle poison.
a. Characterized by skill or ingenuity; clever.
b. Crafty or sly; devious.
[Middle English sotil, from Old French, from Latin subtīlis; see teks- in the Appendix of Indo-European roots.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.