A word appearing in notes from the late 1960s described as “light-substance” (NM/280), “light as an ethereal substance” (NM/283), or “liquid light” (NM/285), derived from the root √LIK “glide, slip, slide, drip” (NM/285). As Tolkien described it:

Q. linque (n., adj.) “(bright/clear/gleaming) liquid”. This was applied (in Quenya) to dew (or to fine rain in sunshine); in Sindarin to pools or rills of clear clean water. It was probably in origin a “mythological” word — referring to the primitive Elvish conception of “light” as an actual substance (emitted by light-givers, but then independent), though ethereally fine and delicate (NM/285).

As such, it could apply to light itself envisioned as an insubstantial liquid or ethereal substance flowing through the air (photons), or other liquids glistening in the light such as dew or fine rain. This rippling, liquid-like nature of light is surprising compatible with the modern quantum physics behavior of photons as both a particle and a wave, but whether Tolkien intended this is unclear.