That's often true, and there are many domain names that are not in the dictionary that are great developed sites.
In this case you have a word that does not exist in any dictionary. Now it could be used in a possesive conotation as in "horse racing's finest" or "F1 racing's best driver" however on it's own it means little. Added in the fact that it's a .org and you have, in my opinion, a $0 value as an undeveloped domain name.
racingsbest.org or racingsfinest.org would be better names, but again, only if developed.