You still like meta keywords for search engine in 2014?
Currently, there is no any impact on SEO with meta keywords.
If you can, read some new articles about SEO. It may help you to get ideas about new search engines algorithams.
For better SEO options, you can install different SEO plugins from http://wordpress.org/plugins/. May some of them have option to add meta Keywords. But it is 100% waste for SEO & it don’t have any impact on your SEO.