In linguistics, blocking refers to the morphological phenomenon in which a possible form for a word cannot surface because it is "blocked" by another form whose features are the most appropriate to the surface form's environment. More basically, it may also be construed as the "non-occurrence of one form due to the simple existence of another." Blocking may also prevent the formation of words with existing synonyms, particularly if the blocked form is morphologically complex and the existing synonym is morphologically simple, e.g. *stealer which is blocked by the existing simple form thief.