Within the framework of Conversation Analysis for Second Language Acquisition (CA-SLA), this study uses learning behavior tracking (LBT) (Markee, 2008) with longitudinal data to investigate word learning by one adult second language (L2) user of English. The adult is a first language (L1) user of Japanese with limited proficiency in English. Data are drawn from audio-recorded conversations-for-learning (Kasper, 2004) between this adult and the researcher, an L1 user of English and L2 user of Japanese, across a 7-month period. The analysis focuses on the learning of the word "near" and the nonuse of the synonym "close". Repair work is found to create opportunities for learning. It is argued that a word is likely to be learned if it is found to be immediately useful. Methodologically, this study shows that CA-SLA used with longitudinal data can be used to investigate word learning, meeting the criteria developed by Ellis (2010) for showing learning.