Usage Note: The verb enthuse, a back-formation from enthusiasm, is viewed as an irritant by many. The sentence The majority leader enthused over his party's gains was rejected by 76 percent of the Usage Panel in our 1982 survey, by 65 percent in 1997, and by 66 percent in 2009. Back-formations often meet with disapproval on their first appearance and only gradually become accepted. For example, diagnose, which was first recorded in 1861, is a back-formation from diagnosis and is perfectly acceptable today. Since enthuse dates from 1827, there may be something more at play here than a slower erosion of popular resistance. Unlike enthusiasm, which denotes an internal emotional state, enthuse denotes either the external expression of emotion (as in She enthused over attending the Oscar ceremonies) or the inducement of enthusiasm by an external source (as in He was so enthused about the diet pills that he agreed to do a testimonial in a television ad). It is possible that a distaste for this emphasis on external emotional display and emotional manipulation is sometimes the source of distaste for the word itself.