A modillion is an ornate bracket, more horizontal in shape and less imposing than a corbel.
They are often seen underneath a cornice which helps to support them.
Modillions are more elaborate than dentils (literally translated as small teeth).
[1] All three are selectively used as adjectival historic past participles (corbelled, modillioned, dentillated) as to what co-supports or simply adorns any high structure of a building, such as a terrace of a roof (a flat area of a roof), parapet, pediment/entablature, balcony, cornice band or roof cornice.
Modillions occur classically under a Corinthian or a Composite cornice but may support any type of eaves cornice.