Something that is subtle is not obvious: a professional food taster might be able to perceive subtle differences of flavor that most people don't notice.

Subtle is used for things that are hard to describe because of their complexity or delicacy: a way of thinking, arguing, or creating a work of art. The word is pronounced like "suttle" and it was originally spelled that way when it was borrowed from Old French, but the b got imported to make the word look more like its ultimate source, the Latin adjective subtilis. If you try to pronounce the b, your ignorance of how to say the word properly won't be very subtle!

Definitions of subtle

adj difficult to detect or grasp by the mind or analyze

“his whole attitude had undergone a subtle change”
“a subtle difference”
imperceptible to the senses or the mind

adj able to make fine distinctions

“a subtle mind”
having the ability to perceive or understand; keen in discernment

adj working or spreading in a hidden and usually injurious way

“a subtle poison”
insidious, pernicious
causing or capable of causing harm

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