Sourest

adjective

1. Having an acidic, sharp or tangy taste.

   "Lemons have a sour taste."

2. Made rancid by fermentation, etc.

   "Don't drink that milk; it's turned sour."

3. Tasting or smelling rancid.

   "His sour breath makes it unpleasing to talk to him."

4. (of a person's character) Peevish or bad-tempered.

   "He gave me a sour look."

5. (of soil) Excessively acidic and thus infertile.

   "a sour marsh"