The related verb, to desiderate (something) is to feel (it) to be lacking, to regret (its) absence. [H. W.] Fowler gives us a warning about this word. He describes it as " . . .a useful word in its place, but . . . so often misplaced that we might be better without it. Readers . . . do not know the meaning of it, taking it for [a] pedantic or facetious form of desire . . . Writers . . . are ill-advised in using the word unless they are writing for readers as learned as themselves. . . ." What one desiderates is a desideratum. --Schur, Norman. 2000 Most Challenging and Obscure Words. New York: Galahad Books, 1994.
Henry Watson Fowler (1858-1933) is a legendary figure and his Dictionary of Modern English Usage (MEU), first published in 1926, is one of the most celebrated reference books of the twentieth century.
--Birchfield, R. W. "Preface to the Third Edition," The New Fowler's Modern English Usage, Third Edition. New York: Oxford University Press, 1996.