Icing is the sweet coating spread over a cake. Pipe the icing, royal icing, icing sugar.
Royal icing sets hard and buttercream stays soft, which is why one is used for decoration that must hold a shape and the other for eating. Americans say frosting for the soft kind. The icing on the cake means a good thing added to something already good.
1nounicingThe sweet coating spread over a cake.
“She covered the birthday cake with pink icing.”
icing is a coating.
Also accepted in games: frosting
The gerund of the verb ice, from the resemblance of the white coating to ice.
Gerund of the verb ice.
Etymology from Wiktionary, CC BY-SA