suc·cess·ful \-esfəl\adjective 1.: resulting or terminating in success : having the desired effect < a successful experiment > 2.: gaining or having gained success; especially: having attained wealth, position, or fame < a successful writer > < a successful banker > 3.of a plant or animal group: represented by diverse forms and occupying a wide variety of ecological niches • suc·cess·ful·ly\-fəlē, -li\adverb • suc·cess·ful·nessnoun-es