Subtle vs. Subtil — Which is Correct Spelling?

(especially of a change or distinction) so delicate or precise as to be difficult to analyse or describe

Making use of clever and indirect methods to achieve something

Crafty; cunning

So slight as to be difficult to detect or describe; elusive

Difficult to understand; abstruse

Able to make fine distinctions

Operating in a hidden, usually injurious way; insidious

Characterized by skill or ingenuity; clever.

Crafty or sly; devious.

Hard to grasp; not obvious or easily understood.

Barely noticeable, not obvious, indistinct.

(of a thing) Cleverly contrived.

(of a person or animal) Cunning, skillful.

Insidious.

Tenuous; rarefied; of low density or thin consistency.

(obsolete) Refined; exquisite.

Sly in design; artful; cunning; insinuating; subtile; - applied to persons; as, a subtle foe.

Cunningly devised; crafty; treacherous; as, a subtle stratagem.

Characterized by refinement and niceness in drawing distinctions; nicely discriminating; - said of persons; as, a subtle logician; refined; tenuous; sinuous; insinuating; hence, penetrative or pervasive; - said of the mind; its faculties, or its operations; as, a subtle intellect; a subtle imagination; a subtle process of thought; also, difficult of apprehension; elusive.

Smooth and deceptive.

Be difficult to detect or grasp by the mind;

Faint and difficult to analyze;

Able to make fine distinctions;

Working or spreading in a hidden and usually injurious way;