moodyoudaoicibaDictYouDict[mood 词源字典]
mood: English has two words mood. The original one, ‘emotional state’ [OE], goes back to a prehistoric Germanic *mōthaz or *mōtham, whose descendants have denoted a wide range of such states: ‘anger’, for instance (Old Norse móthr), and ‘courage’ (German mut). Old English mōd meant ‘mind, thought’, ‘pride’, ‘courage’, and ‘anger’ as well as ‘frame of mind’, but it is only the last that has survived. Mood ‘set of verb forms indicating attitude (such as the subjunctive)’ [16] is an alteration of mode, influenced by mood ‘frame of mind’.
=> mode[mood etymology, mood origin, 英语词源]
mood (n.1)youdaoicibaDictYouDict
"emotional condition, frame of mind," Old English mod "heart, frame of mind, spirit; courage, arrogance, pride; power, violence," from Proto-Germanic *motha- (cognates: Old Saxon mod "mind, courage," Old Frisian mod "intellect, mind, intention," Old Norse moðr "wrath, anger," Middle Dutch moet, Dutch moed, Old High German muot, German Mut "courage," Gothic moþs "courage, anger"), of unknown origin.

A much more vigorous word in Anglo-Saxon than currently, and used widely in compounds (such as modcræftig "intelligent," modful "proud"). To be in the mood "willing (to do something)" is from 1580s. First record of mood swings is from 1942.
mood (n.2)youdaoicibaDictYouDict
"grammatical form indicating the function of a verb," 1560s, an alteration of mode (n.1), but the grammatical and musical (1590s) usages of it influenced the meaning of mood (n.1) in phrases such as light-hearted mood.