def make_word_groups(vocab_words: str) -> str:
    """
    This function takes a `vocab_words` list and returns a string
    with the prefix  and the words with prefix applied, separated
    by ' :: '.

    Args:
        vocab_words (str): list of vocabulary words with a prefix.

    Returns:
        str: str of prefix followed by vocabulary words with
             prefix applied, separated by ' :: '.
    """

    prefix = vocab_words[0]

    output = prefix
    for word in vocab_words[1:]:
        output += " :: " + prefix + word
    return output