1.  emulsion(n = noun.substance) - (chemistry) a colloid in which both phases are liquids; "an oil-in-water emulsion"
is a kind of colloid
Derived forms verb emulsify₂, verb emulsify₁

2.  emulsion(n = noun.artifact) photographic emulsion - a light-sensitive coating on paper or film; consists of fine grains of silver bromide suspended in a gelatin;
is a kind of coat, coating
Derived forms verb emulsify₂, verb emulsify₁

   Any liquid preparation of a color and consistency resembling milk; as: (a) In pharmacy, an extract of seeds, or a mixture of oil and water united by a mucilaginous substance. (b) In photography, a liquid preparation of collodion holding salt of silver, used in the photographic process. [1913 Webster]

emulsion, n.
1 a fine dispersion of one liquid in another, esp. as paint, medicine, etc.
2 a mixture of a silver compound suspended in gelatin etc. for coating plates or films.

Idiom:
emulsion paint a water-thinned paint containing a non-volatile substance, e.g. synthetic resin, as its binding medium.

Derivative:
emulsionize v.tr. (also -ise). emulsive adj.

Etymology:
F {eacute}mulsion or mod.L emulsio f. emulgere (as E-, mulgere muls- to milk)

N  semiliquidity, stickiness, viscidity, viscosity, gummosity, glutinosity, mucosity, spissitude, crassitude, lentor, adhesiveness, inspissation, incrassation, thickening, jelly, mucilage, gelatin, gluten, carlock, fish glue, ichthyocol, ichthycolla, isinglass, mucus, phlegm, goo, pituite, lava, glair, starch, gluten, albumen, milk, cream, protein, treacle, gum, size, glue (tenacity), wax, beeswax, emulsion, soup, squash, mud, slush, slime, ooze, moisture, marsh, semifluid, semiliquid, tremellose, half melted, half frozen, milky, muddy, lacteal, lactean, lacteous, lactescent, lactiferous, emulsive, curdled, thick, succulent, uliginous, gelatinous, albuminous, mucilaginous, glutinous, glutenous, gelatin, mastic, amylaceous, ropy, clammy, clotted, viscid, viscous, sticky, tacky, gooey, slab, slabby, lentous, pituitous, mucid, muculent, mucous, gummy.

photographic emulsion