From Longman Dictionary of Contemporary Englishpiepie /paɪ/ ●●● S2 noun [countable, uncountable] 1 
DFfruit baked inside a pastry coveringslice/piece of pie Would you like another piece of apple pie?2 British EnglishDF meat or vegetables baked inside a pastry or potato covering I had steak and kidney pie with chips.3 → slice/share/piece of the pie4 → pie in the sky
DFfruit baked inside a pastry coveringslice/piece of pie Would you like another piece of apple pie?2 British EnglishDF meat or vegetables baked inside a pastry or potato covering I had steak and kidney pie with chips.3 → slice/share/piece of the pie4 → pie in the skyExamples from the Corpus
pie• On Monday night the club's members are looking forward to a pie and peas supper.• cherry pie• Should they compromise with Clinton over a piece of the tax-cut pie or hold out for the whole pie?• Often after lavish feasting, enormous pies would be brought to the banquet table.• Eat humble pie and get used to it mate.• Line 9-inch pie pan with 1 / 2 dough and arrange yam slices on it.• steak and kidney pie• A large number of young men reported eating white bread, chips, meat pies and sweets regularly.• a piece of pie• I had my finger in the policy pie, as well.• Lay on a pork pie buffet.slice/piece of pie• With some of the money he got, he bought a piece of pie and a cup of coffee.• So I had a slice of pie and then he put the kettle on for coffee and went to the loo.• He lost his appetite for a girlfriend two seasons ago when she refused to share a piece of pie with him.Origin pie (1300-1400) Perhaps from pie “magpie” ( → MAGPIE); because the different things in a pie are like the different things a magpie collects 