Diaphanous
Etymology
From Medieval Latin diaphanus, from Greek diaphanēs, "transparent," built on dia-, "through," and phainein, "to show" — literally "showing through." It was long a technical term for transparent materials before settling into its literary use for filmy, delicate, near-transparent things. The core image is unchanged: something so fine that what lies behind it shows through.
adjective · /dy-AF-uh-nus/
So light, delicate, and fine as to be almost transparent.
What it names
The gauzy, see-through delicacy of fabric, wings, or mist — thin enough that light passes through it.
Example
The curtains were diaphanous, dissolving the morning light into a soft, uniform glow.
Related idea
Translucent lets light through while blurring what is behind it; diaphanous stresses fine, filmy delicacy, usually of fabric or wings.