形容词

1. 不易察觉的;不明显的;微妙的
Something that is subtle is not immediately obvious or noticeable.

1. working or spreading in a hidden and usually injurious way

e.g. glaucoma is an insidious disease
a subtle poison

Synonym: insidiouspernicious

2. difficult to detect or grasp by the mind or analyze

e.g. his whole attitude had undergone a subtle change
a subtle difference
that elusive thing the soul

Synonym: elusive

3. able to make fine distinctions

e.g. a subtle mind