What is the meaning of the word "sad"?

Definitions:

An emotional state characterized by feelings of unhappiness, disappointment, grief or sorrow, often associated with negative experiences, loss, or lack of fulfillment in various aspects of life. ADJECTIVE
- He looked so sad sitting alone in the park.
Describes a feeling of unhappiness, sorrow, or emotional pain, or something that causes or reflects those feelings. ADJECTIVE
- I was feeling sad because my dog had died.
- She felt sad after saying goodbye to her friend.
Experiencing or showing sorrow, grief, or unhappiness. ADJECTIVE
- His eyes looked sad, even when he smiled.