sadness

n. unhappiness, despondency; regretfulness, state of being filled with grief

Sadness is a mood that displays feeling of disadvantage and loss. Deep immersion in this feeling may lead eventually to clinical depression, a pathological state which may require intervention by a qualified professional. Usually while in a state of sadness, the person becomes quiet, less energetic and withdraws into oneself. He has neither the urge to go out and be active nor the desire to socialize with others. Visual symptoms of sadness are a downcast appearance of the head, a sloping body, and slow and weak physical activity. Sadness is considered as an opposite feeling to happiness. Synonyms to this feeling are sorrow, grief, unhappiness, misery, melancholy and gloom. According to the philosopher Baruch Spinoza there are three basic feelings: passion, happiness and sadness. Spinoza defined sadness as the “transfer of a person from a large perfection to a smaller one”.
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SAD seasonal affective disorder. SAD abbr. seasonal affective disorder Seasonal affective disorder Amooddisorder characterized by depression during [more]Sadness - Community and Resources

Noun
1. emotions experienced when not in a state of well-being
(synonym) unhappiness
(antonym) happiness
(hypernym) feeling
(hyponym) dolefulness
2. the state of being sad; "she tired of his perpetual sadness"
(synonym) sorrow, sorrowfulness
(hypernym) unhappiness
(hyponym) mourning, bereavement

(n.)
Seriousness; gravity; discretion.
  

(n.)
Quality of being sad, or unhappy; gloominess; sorrowfulness; dejection.
  

(n.)
Heaviness; firmness.