$suffixes = array(
    '(\X{2,})(ões)\b',
    '(\X{4,})(s)\b',
    '(\X{3,})(es)\b',
    '(\X{3,})(ns)\b',
    '(\X{2,})(éis)\b,
    '(\X{2,})(óis)\b',
    '(\X{2,})(ães)\b'
);
preg_replace($suffixes, '\1', $text);