Using the Python Objective-C bindings, you could create just a small python script to get it from the built in OS X Dictionary. Here's a post that details this script"
from DictionaryServices import *
searchword = sys.argv.decode('utf-8')
errmsg = 'You did not enter any terms to look up in the Dictionary.'
wordrange = (0, len(searchword))
dictresult = DCSCopyTextDefinition(None, searchword, wordrange)
if not dictresult:
errmsg = "'%s' not found in Dictionary." % (searchword)
if __name__ == '__main__':
Save that to
dict.py, and then just run
python dict.py dictation
Check out the post for more instructions on making it accessable all across your terminal.