Mood, humor, temper, vein mean a temporary state or frame of mind in which one emotion or desire or one set of emotions gains the ascendancy.
Mood is the comprehensive term for any such frame of mind, regardless of its particular cause, its particular character, its effect on others, or its length of existence.
Mood carries a stronger implication of pervasiveness and of compelling power than the other terms; also, it may refer not only to the frame of mind, but to its expression in a literary or artistic work or to what is seen or heard in such a way as to evoke a mood or to harmonize with one's mood.
Humor (see also WIT 2 ) applies chiefly to a mood which is the result of one's peculiar temperament or of one's physical or mental condition at the moment; it may be preferable to mood when the idea of capriciousness or of whimsicality is to be suggested.
Temper (see also DISPOSITION 2 ) applies to a mood dominated by a single strong emotion, often specifically that of great anger. When qualified by an adjective indicating the controlling emotion, temper may apply to any humor that manifests itself in a display of feeling.
Vein (see also TOUCH ) is often used in the sense of mood but with a stronger implication of transitoriness and seldom with any suggestion of a temperamental or physical basis.