Definitions of bitter:

• noun:   the taste experience when quinine or coffee is taken into the mouth
• noun:   English term for a dry sharp-tasting ale with strong flavor of hops (usually on draft)
• noun:   the property of having a harsh unpleasant taste
• verb:   make bitter
• adjective:   proceeding from or exhibiting great hostility or animosity

  Example: "A bitter struggle"

• adjective:   expressive of severe grief or regret

  Example: "Shed bitter tears"

• adjective:   one of the four basic taste sensations; sharp and disagreeable; like the taste of quinine
• adjective:   very difficult to accept or bear

  Example: "The bitter truth"

• adjective:   causing a sharply painful or stinging sensation; used especially of cold

  Example: "Bitter cold"

• adjective:   marked by strong resentment or cynicism

  Example: "Bitter about the divorce"

• adjective:   harsh or corrosive in tone

  Example: "Bitter words"

• adverb:   extremely and sharply

  Example: "It was bitterly cold"

• name:  A surname (rare: 1 in 100000 families; popularity rank in the U.S.: #18335)