an unpleasant taste or smell► horrible/disgusting/revolting very bad - use this especially to talk about things that taste, smell, or look really bad: · It was the most disgusting meal I've ever eaten.· He smiled showing his teeth, which were a revolting yellow colour.· What a horrible smell!· Dick had cooked a special stew, which looked and smelled revolting.
► unpleasant tasting or smelling horrible: · Undercooked potatoes taste unpleasant and can be harmful.· Some animals give off an unpleasant odor that deters attackers.
► foul a foul smell or taste is extremely bad, and is caused especially by waste or things decaying: · There was a foul smell coming up from the river.
► gross informal very unpleasant - use this to talk about food, smells, or behaviour that you dislike very much: · Ooh, gross! I hate spinach!· Brad threw up on the floor at the party. It was really gross.
► not very nice British /not very good/not too good spoken a taste or smell that is not very nice or not very good is slightly unpleasant: · This cheese isn't very good. How long have we had it?· The first time I smoked a cigarette it didn't taste very nice.· I wouldn't cook that if I were you. It doesn't smell too good.
► nasty tasting or smelling very strong and unpleasant: · I'm not very keen on this wine. It has a nasty aftertaste.· Police were alerted when neighbors complained of a nasty smell coming from the basement.· Cheap perfume often smells nasty after a couple of hours.
► unappetizing a meal or food that is unappetizing has an unpleasant appearance or smell and does not make you want to eat it: · The soup was cold and unappetizing, but it was all there was.· The main course was an unappetizing leg of chicken with boiled potatoes.
food that is unappetizing has an unattractive appearance that makes you think that it will not taste good: 
a rather unappetizing egg sandwich