Longman Dictionary of Contemporary English
Wiktionary
n. A prop used in slapstick consisting of an open pie filled with custard or cream (or, more often nowadays, simply a paper plate covered with shaving foam or a similar substance) that is pushed into another person's face
WordNet
n. a prop consisting of an open pie filled with real or artificail custard; thrown in slapstick comedies
Wikipedia
"Custard Pie" is the opening track on the English rock band Led Zeppelin's sixth album, Physical Graffiti, released in 1975.
Custard Pie is a Canadian situation comedy television series which aired on CBC Television in 1977.
Usage examples of "custard pie".
Dressed in a spangled gown, Celandine paraded, showing the audience a huge custard pie.
This did not bode well for an evening of thespianic splendor, although there was always the possibility that one of them might hit another one in the face with a custard pie.
What happened was that life dropped a big custard pie on us, and that's not my fault.
The detective gazed at the cash as longingly as a glutton might stare at a custard pie, as intensely as a satyr might ogle a naked blonde.
He ate a piece of pumpkin pie and a piece of custard pie, and he ate almost a piece of vinegar pie.
If it didn't have a custard pie in it somewhere, they said, it wasn't funny.