In this work, the morphological process present in the formation of denominal verbs -ar in Brazilian Portuguese and the suitable syntactic and semantic implications that come from these process are studied. Proposals that traditionalist, structuralist, diachronically oriented and generativist linguists present about the process of suffix derivation in nouns or verbs are analyzed. Nominal bases of denominal verbs are examined, as well as the process of suffix derivation on verbs and nouns, in connection with the subsequent study of the process of conversion in Brazilian Portuguese. At the same time, the morphological nature is discussed of the thematic vowel -a, which occurs both in first conjugation verbs and thematic nouns in Portuguese, given the controversy as to whether Xar denominal verbs are formed by conversion rather than by suffix derivation. Beyond denominal verbs, deverbal nouns and nominalized forms of verbs are also analyzed, and a morphological basis of directionality for denominal verb formation and deverbal forms is proposed. Additionally to the morphological aspect of denominal verb formation the semantic condition of the nominal bases and suffixes that are embedded in the formation of new lexis is considered, since there is in language a narrow correlation between syntax, semantics and morphology.