The verb enthuse, formed via backformation from the adjective enthusiastic, peeves some people who care about English usage, but the word has been in the language long enough to gain acceptance. We might not like it, but it’s a word.
Similar backformations such as donate (from donation) and diagnose (from diagnosis) are now unquestioned. Whether enthuse will gain a similar level of acceptance is impossible to say, but the word has been around for over a century, so maybe the issue is already settled.
With enthuse, however, problems arise when enthused is used as a past-participle adjective in place of enthusiastic, which is a perfectly good, and far older, word. Plus, the adjective enthused can carry an ironic tone and is difficult to use in earnest.
Examples
In these examples, enthused is used where enthusiastic would work just as well:
Not only am I sold on the new Pentastar engine, I am totally enthused on all the new Chrysler products. [letter to Globe and Mail]
I was never too enthused about big bookstores like Borders. [comment on Washington Post]
So when word circulated that Lee would become consulting chef for Eden South Beach, Miami locals were naturally enthused. [Miami New Times]
And in these, enthuse is easier to justify because it’s used as a verb (although one could argue there are superior words for these purposes):
Way to the other side of the political spectrum, Pat Buchanan has enthused about the “Tea Party Tory” now in Number 10 Downing Street. [The Algemeiner]
It was particularly amusing to watch all the models enthuse about how CSI is one of the longest-lived franchises on TV . . . [AV Club]
Charities will be able to bid for contracts worth millions, they enthuse. [The Economist]
