Tart (6)
'tart' is the definition.
(both can mean bitter-tasting)
This is all the clue.
(Other definitions for acid that I've seen before include "Sarcastic - tart" , "It is neutralised by alkali" , "Morose" , "Substance with pH of less than 7" , "Etcher's fluid" .)
'tart' is the definition.
(similar in meaning)
This is all the clue.
(Other definitions for sour that I've seen before include "Acrid or sullen" , "Tasting sharp like stale milk" , "Sharp- or tart-tasting" , "Acid-tasting" , "Turned - morose" .)
'tart' is the definition.
(type of tart)
This is all the clue.
(Other definitions for flan that I've seen before include "dish, sweet or savoury" , "Open-topped pie" , "Baked dish filled with fruit or custard" , "Open-topped pastry dish" , "Open pastry case with savoury filling" .)
'tart' is the definition.
(both are baked goods)
This is all the clue.
(Other definitions for pie that I've seen before include "Easy thing" , "Small, former coin of India" , "In the sky, this dish is impractical" , "Food baked under pastry" , "Pastry-crust savoury" .)
'tart' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for bitter that I've seen before include "Sour tasting, like English ale" , "Unpalatable; a beer" , "Kind of British beer" , "Not sweet; very cold" , "Resentful or angry through disappointment" .)