def create_histogram_dict(words_list):
    """Return a dictionary representing a histogram of words in a list.

       Parameters:
       words_list(list): list of strings representing words

       Returns:
       histogram(dict): each key a unique word, values are number of
       word appearances

    """
    histogram = dict()
    words = histogram.keys()
    for word in words_list:
        if word.lower() not in words:
            histogram[word.lower()] = 1
        else:
            histogram[word.lower()] += 1
    return histogram