from typing import List


def merge_words(word_matrix: List[List[str]]) -> List[str]:
    """
    Merge lists of lists into one list.
    :param word_matrix:
    :return:

    >>> merge_words([['kai', 'gar', 'onar'], ['ek', 'Dios', 'esti']])
    ['kai', 'gar', 'onar', 'ek', 'Dios', 'esti']

    """
    if not word_matrix:
        return word_matrix  # type: ignore
    return [item for items in word_matrix for item in items]