The Skip-gram with negative sampling (SGNS) method of Word2Vec is an unsupervised approach to map words in a text corpus to low dimensional real vectors. The learned vectors capture semantic relationships between co-occurring words and can be used as inputs to many natural language processing and machine learning tasks. There are several high-performance implementations of the Word2Vec SGNS method. In this paper, we introduce a new optimization called context combining to further boost SGNS performance on multicore systems. For processing the One Billion Word benchmark dataset on a 16-core platform, we show that our approach is 3.53x faster than the original multithreaded Word2Vec implementation and 1.28x faster than a recent parallel Word2Vec implementation. We also show that our accuracy on benchmark queries is comparable to state-of-the-art implementations.