Pellucid

Etymology

From Latin pellucidus, from per-, "through," and lucēre, "to shine" — light shining all the way through. It first described physically transparent things like water or crystal, then extended to writing and thought that are perfectly clear and easy to follow. The metaphor of clarity as light passing unobstructed is ancient and still vivid.

adjective · /peh-LOO-sid/
Transparently clear, whether physically or in expression.
What it names
The quality of being so clear that light or meaning passes straight through — used both of water and glass and of lucid, effortless prose.
Example
What makes the essay so persuasive is its pellucid argument, each step visible and impossible to misread.
Related idea
Limpid stresses untroubled, serene clearness, often of water or eyes; pellucid emphasizes clarity you can see or understand straight through.