"Subtilis" itself is a combination of "sub", meaning "under" or "below", and "tilis", which means "fine" or "thin".
Therefore, the literal meaning of "subtilis" is "underneath fine" or "below the surface".
Over time, the meaning of "subtle" has evolved to encompass the following nuances:
* Delicate or refined: This sense reflects the original meaning of "fine" or "thin".
* Difficult to perceive or understand: This meaning emphasizes the idea of something being "below the surface" and requiring careful attention to detect.
* Cunning or sly: This usage alludes to the notion of being "underhanded" or "secret".
So, the word "subtle" has a long and interesting history, rooted in the Latin concept of something being both delicate and hidden.