Spoken language data were collected from six adult second language (L2) English learners over a year-long period in order to explore the development of word polysemy and frequency use. The data were analyzed both quantitatively and qualitatively. In the first analysis, the growth of WordNet polysemy values and CELEX word frequency values were examined. For both indexes, significant growth was demonstrated from the 2nd to the 16th week of observation, after which values remained stable. Growth in word polysemy values also correlated with changes in word frequency, supporting the notion that frequency and polysemy effects in word use are related. A second analysis used the WordNet dictionary to explore qualitative changes in word sense use concerning six frequent lexical items in the learner corpus (think, know, place, work, play, and name). A qualitative analysis compared normalized frequencies for each word sense in the first trimester of the study to the later trimesters. Differences in the number of word senses used across trimesters were found for all six words. Analyses 1 and 2, taken together, support the notion that L2 learners begin to use words that have the potential for more senses during the first 4 months; learners then begin to extend the core meanings of these polysemous words. These findings provide further insights into the development of lexical proficiency in L2 learners and the growth of lexical networks.