adjective
This apple has a pleasant, slightly sour taste. Do you like sour dill pickles?
If the food is sour, throw it away
The poor service and facilities made the entire holiday a very sour experience
The waitress's sour expression matched her sour disposition
verb
Milk sours quickly in this climate if you don't refrigerate it
Being forced to practise for hours when a child was what soured my enjoyment of playing the piano
US