Why blacklist rather than whitelist?

    LC_ALL=C egrep '^[[:lower:]]{4,8}$' /usr/share/dict/words |
    shuf --random-source=/dev/random -n4 |
    fmt

That's picking from ~35,000 words, which I think is still good enough but avoids ending up with "interpreters incredibility disciplinary constitutionality". (I need the C locale to stop this old GNU grep being painfully slow.)