Back- formation in English is one of the processes of word-formation, whereby new verbs are derived from already existing nouns by deleting what is thought to be a suffix. In Arabic, the case is different; back-formation is considered a derivational process called ¿¿¿¿¿¿¿¿ ¿¿ ¿¿¿¿¿ ¿derivation from the noun¿ in which new verbs are formed by applying the processes of affixation, infixation and substitution. In other words, in English it is a deletion process whereas in Arabic it is a process of addition and modification. Antonomasia is another word-formation process in English, in which new verbs, nouns and adjectives are derived from proper names. In Arabic, antonomasia is a ¿¿¿¿¿¿¿¿ ¿¿ ¿¿¿¿¿ under subsumed process derivational whereby only verbs can be derived from proper names. The present contrastive study investigates the two word-formation processes back-formation and antonomasia in English and their Arabic counterparts, so as to shed light on the points of similarity and difference between the two languages. The present study is based on the following hypotheses: 1. The points of difference between English back-formation and its Arabic counterpart are more than the points o