http://www.law.cornell.edu/uscode/html/uscode15/usc_sec_15_00001125----000-.html http://www.law.cornell.edu/uscode/html/uscode15/usc_sec_15_0... In the US, one

http://www.law.cornell.edu/uscode/html/uscode15/usc_sec_15_00001125----000-.html http://www.law.cornell.edu/uscode/html/uscode15/usc_sec_15_0... In the US, one at a time - but there could be a class of names which are confusingly similar to that name. They either need to argue that the similarity "is likely to cause confusion, or to cause mistake, or to deceive as to the affiliation, connection, or association of such person with another person, or as to the origin, sponsorship, or approval of his or her goods, services, or commercial activities by another person" or dilution by blurring an "association arising from the similarity between a mark or trade name and a famous mark that impairs the distinctiveness of the famous mark". The second (trademark dilution) only applies to famous marks (like Facebook), but can be used when the mark is only diluted, and there is no likelihood of confusion. However, "the degree of inherent or acquired distinctiveness of the famous mark" is important - and the distinctiveness isn't just in one particular market. English words are unlikely to be considered to be particularly distinctive, and 'face books' existed on paper before Facebook used the term.