Why does speech recognition take up 1 GB or RAM suddenly? And Gmail in Safari 738 MB?
You can kill this process (in terminal or activity monitor), and it seems as long as the Dictation &amp; Speech pref pane (Yosemite) has dictation and enhanced dictation off and the pref pane is not open, it won't re-spawn.

See for ref:

http://www.mcelhearn.com/os-x-10-9-mavericks-enhanced-dictation-is-a-memory-hog-and-doesnt-work-very-well/

https://discussions.apple.com/thread/5824504