Word History: Physicians in ancient and medieval times thought that the human body contained a mixture of four fluids and that a person's health and temperament depended upon the relative proportions of these fluids within the body. In Middle English, these fluids were called humours, ultimately from the Latin word hūmor, "fluid." (Latin hūmor, also found in the variant form ūmor, contains the same root found in the Latin adjective hūmidus, "moist," whence English humid.) Each of the four humors, namely blood, phlegm, black bile, and yellow bile, or sanguis, phlegma, melancholia, and choler in Latin, were defined as warm or cold and moist or dry and associated with one of the four elements, and a superfluity of any one humor was thought to produce a characteristic disposition. Blood, the warm, moist humor associated with the element fire, caused a ruddy complexion and a sanguine disposition, marked by courage, hope, and a readiness to fall in love. Phlegm, the cold, moist humor associated with water, made one phlegmatic, or calm, sluggish, and unemotional. Black bile, the cold, dry humor associated with earth, caused depression, or melancholy. Yellow bile, the warm, dry humor associated with the air, made one choleric, or easily angered. By the late 1500s, the word humour had become synonymous with temperament and was used especially to refer to one's temperament when dominated by one of the four humors. As an extension of this sense, humour came to indicate changing moods or states of mind, particularly whimsical and capricious fancies that, when revealed in action, provide amusement to others. In the 1600s, humour (now spelled humor in the United States) at last came to mean the quality that makes something amusing or laughable, as well as the ability to amuse others and to appreciate those things that are amusing—that is, a sense of humor.