Google does not have a banned word list - as far as I am aware.. and there are many "illegal" and "abhorrent" things you can search on google if you need "proof"
Without knowing the domain name(post it if you feel comfortable).. I will really just be guessing.. but...
It may have been "punished" by google for previous 'bad' use - SE spam etc..
It may simply not have enough inbound links(though this is unlikely - if googlebot has been to the domain)
Thats about all I can say without knowing the domain..
DD