Citi for Citi bank, citi radio, yes.
Citi and how it is used for other brands or branding, yes. A TM is exactly that, a TM as in how it is used to conduct trade or business.
Citi is also a foreign word and can not be trademarked as it is Generic. It is a word within itself.
Same with the word city.
Generic word. Can not be trademarked. Think of the word in two parts...
TRADE MARK.
How both these words are used, their intent, their logo or design can be trademarked. How you plan to use it and if it infringes upon the TM'd versions is another issue.
See definition of trademark:
http://www.uspto.gov/web/offices/ta...DefineTrademark
http://www.uspto.gov/web/offices/pa...eral/whatis.htm
Then this section:
http://tess2.uspto.gov/tmdb/tmep/1200.htm#_T1215
This deals specifically with domain names.
Pay Particular attention to section 1215.05 Generic Refusals
Understand when it is referring to being a "refusal" the USPTO is instructing their own patent attorneys to "refuse" the granting of trademarks "in general the examining attorney should refuse registration on the ground that the mark is generic..." and cite specific examples of the generic word TURKEY and BANK.
Examples of CITI along with the aforementioned banking and credit card institution:
CITI Center for Information Technology Integration (University of Michigan)
CITI Columbia Institute for Tele-Information (Columbia University)
CITI Citoyens d'Internet (French)
CITI Celibacy Is the Issue
CITI Confederation Internationale des Travailleurs Intellectuels (French: International Confederation of Intellectual Workers)
CITI Center for Instructional and Technological Innovation (NJCU)
CITI Chemical Inspection and Testing Institute