Merriam-Webster Collegiate Dictionary - kudo

 noun  (plural ~s)  Etymology: back-formation from ~s (taken as a plural)  Date: 1926  1. award, honor a score of honorary degrees and…other ~s — Time  2. compliment, praise to all three should go some kind of special ~ for refusing to succumb — Al Hine Usage:  Some commentators hold that since ~s is a singular word it cannot be used as a plural and that the word ~ is impossible. But ~ does exist; it is simply one of the most recent words created by back-formation from another word misunderstood as a plural. Kudos was introduced into English in the 19th century; it was used in contexts where a reader unfamiliar with Greek could not be sure whether it was singular or plural. By the 1920s it began to appear as a plural, and about 25 years later ~ began to appear. It may have begun as a misunderstanding, but then so did cherry and pea.