From Longman Dictionary of Contemporary Englishlemonlem‧on1 /ˈlemən/ ●●● S3 noun 1 
[countable, uncountable]HBPDFF a fruit with a hard yellow skin and sour juice a slice of lemon Add a few drops of lemon juice.2 [uncountable] British EnglishDFD a drink that tastes of lemons a glass of fizzy lemon3 [uncountable] (also lemon yellow)CC a pale yellow colour4 [countable] especially American English informalUSELESS something that is useless because it fails to work or to work properly I soon realized the van was a lemon.5 [countable] British English informalSTUPID/NOT SENSIBLE a silly person He just stood there looking like a real lemon.
[countable, uncountable]HBPDFF a fruit with a hard yellow skin and sour juice a slice of lemon Add a few drops of lemon juice.2 [uncountable] British EnglishDFD a drink that tastes of lemons a glass of fizzy lemon3 [uncountable] (also lemon yellow)CC a pale yellow colour4 [countable] especially American English informalUSELESS something that is useless because it fails to work or to work properly I soon realized the van was a lemon.5 [countable] British English informalSTUPID/NOT SENSIBLE a silly person He just stood there looking like a real lemon.Examples from the Corpus
lemon• There are indeed times when a lemon as a seasoning seems second only in importance to salt.• It's also very good made with jam, lemon or cheese.• Most lemons last through mid-April and grapefruit, through mid-June.• I prefer this blend with about 5 drops of bergamot or lemon added to brighten the aroma.• Our van turned out to be a real lemon.• Use lime juice or zest rather than lemon.lemonlemon2 (also lemon yellow) adjective pale yellow in colourExamples from the Corpus
lemon• Mix the lemon juice and vanilla essence with the custard.• Mix the yogurt with the lemon juice, mint and parsley and season to taste with the salt and black pepper.• If the mixture seems too dry, add a little more olive oil and lemon juice.• And they ate Papparadelle Ripiene stuffed with goat cheese and Parmesan and covered with a grated lemon peel and cream sauce.• Hot-pressed sandwiches such as basil, mozzarella and tomato; lemon turkey; smoked salmon; and roast beef.Origin lemon (1300-1400) French limon, from Medieval Latin limo, from Arabic laymun 