Words that Should Exist
but perhaps don't yet

The Dictionary of Obscure Sorrows John Koenig

The Meaning of Liff: The Original Dictionary Of Things There Should Be Words For Douglas Adams

The Deeper Meaning of Liff: A Dictionary of Things There Aren't Any Words for Yet--But There Ought to Be Douglas Adams and John Lloyd

Predicting New Words: The Secrets of Their Success Allan Metcalf

Anguish Languish Howard L Chace (see Wikipedia article, and Project Gutenberg version)