douceur

Sweetness of manner: agreeableness, gentleness.

Sweet speech: a compliment.

A sweetener: a gift offered to sweeten another's attitude, a tip or bribe.

When Dangerfield put the little roll in his hand, Irons looked suspicious and frightened, and balanced it in his palm, as if he had thoughts of chucking it from him, as though it were literally a satanic douceur. But it is hard to part with money, and Irons, though he still looked cowed and unhappy, put the money into his breeches' pocket, and he made a queer bow […]

A tax break provided as an inducement to sell valuable items (especially art) to public collections rather than on the open market.