A suffix dictionary lists and describes all existing suffixes, providing readers with information on what a given suffix signifies as a word modifier. It also helps readers to select the most appropriate suffix with which to modify a given word stem. A suffix is a letter or series of letters that, when placed after a word stem, creates a new word. For example, the word stem "govern" can be modified with the suffix "-ment" to form the new word "government."
Suffixes either carry grammatical information or lexical information; these two classifications of suffixes are referred to, respectively, as "inflectional" and "derivational" suffixes. Inflectional suffixes never change the class of a word; for example, verbs modified by inflectional suffixes will always remain verbs. Derivational suffixes often change the word class of a word. Suffixes are not always simply added to the end of a word, and sometimes involve a change in the word stem itself, such as in "happy" becoming "happiness," rather than "happyness," when modified with the suffix "-ness."
The word "walk" may be modified with inflectional suffixes such as "-s," "-ed," or "-ing" to create the new words "walks," "walked," and "walking." In all of these examples, the word stem "walk" remains a verb.
The word "child," when modified with the derivational suffix "-less" to create the word "childless," is transformed from a noun into an adjective. However, "child" may also be modified with the derivational suffix "-hood" to create the word "childhood," which retains its classification as a noun.