pip install pyobjc-framework-DictionaryServices && ln -s ./dict.py /usr/bin/dict

dict.py

#!/usr/bin/python
import re
import sys
from DictionaryServices import DCSCopyTextDefinition

split_re = re.compile(r"\s+(?=[A-Z]\.\s)")
_split_re = re.compile(r"(?=" + u"[\u2460-\u2473]" + r")")


def search(word):
    wordrange = (0, len(word))
    search_result = DCSCopyTextDefinition(None, word, wordrange)

    if not search_result:
        errmsg = "'%s' not found in system dict." % (word)
        print errmsg.encode('utf-8')
        sys.exit(2)

    else:
        return search_result.encode('utf-8')


def format(search_result):
    _fresult = split_re.sub('\n\n', search_result)
    fresult = _split_re.sub('\n    ', _fresult.decode('utf-8'))
    return fresult


def main():

    if not len(sys.argv) == 2:
        print 'Usage: dict <word>'
        sys.exit(1)

    word = sys.argv[1].decode('utf-8')
    search_result = search(word)

    print '---------------'
    print format(search_result)
    print '---------------'


if __name__ == '__main__':
    main()