This study conceptualizes lexical sophistication as a multidimensional phenomenon by reducing numerous lexical features of lexical sophistication into 12 aggregated components (i.e., dimensions) via a principal component analysis approach. These components were then used to predict second language (L2) writing proficiency levels, holistic lexical proficiency scores, and longitudinal lexical growth. The results from regression analyses indicated that 5 lexical components (i.e., bigram and trigram strength of directional association, content word properties, bigram mutual information, bigram and trigram proportions, and word specificity) explained 16.1% and 31.0% of the variance of L2 writing proficiency and lexical proficiency, respectively. Two additional components (i.e., word acquisition properties and content word frequency) explained an additional 8.5% of the variance of L2 writing proficiency. Six lexical components (i.e., bigram and trigram proportions, word acquisition properties, content word frequency, bigram frequency and range, content word properties, and function word frequency and range) showed significant developmental trends in L2 beginning learners over a year-long period. These findings provide information about the multidimensional nature of lexical sophistication by expanding its scope beyond frequency and toward other primary dimensions that include various lexical and phrasal features such as concreteness, orthographic density, hypernymy, and "n"-gram frequency and association strength.