Since Tai Chi originates in the oriental culture, the terms used in describing the body movements in martial art don't have corresponding words in western language. The following section is a selective list of online dictionaries that explains Tai Chi terms in particular and martial art terms in genral. They are good places to go for Tai Chi beginners.

Taijiquan Slovar - http://www.geocities.com/oldyangtaijiquan/slovar.htm
This is an online dictionary that explains the terms representing body movements in Tai Chi.

Wushu dictionary - http://www.thewushucentre.com/wushudictionary.htm
This is an online dictioary that includes the frequently used martial art terms, which are displayed in Chinese characters. It has both English and French translations.

The David Brent Wolfe Dictionary of Martial Art Terms - http://pages.prodigy.net/david_wolfe/pmaa/
This online dictionary is a comprehensive collection of martial art terms used in various countries.

Martial Arts Terms Dictionary: Wushu - http://www.martialarts.com/dictionary/wushu/indexst.htm
This is another neatly organized online dictionary of martial art terms.

Related Dictionaries and Encyclopedias

Gale Encyclopedia of Alternative Therapy - http://www.findarticles.com/g2603/0001/2603000121/p1/article.jhtml
Have a detailed entry on Tai Chi with a focus on its therapeutical effect.

National Institutes for Health - Asian American Health - http://asianamericanhealth.nlm.nih.gov/compmed04.html
Have a few entries on Tai Chi and Qi Gong as alternative medicine.

Alternative Health Dictionary - http://www.canoe.ca/AltmedDictionary/t.html
An online dictionary of "alternative medicine", including Tai Chi and other methods.

Julian F. Pas, Man Kam Leung. Historical Dictionary of Taoism. Scarecrow Press, 1998.
A print dictionary of Taoism, the philosopycal hodbed for Tai Chi.

Werner Wunsche (Translator), Ingrid Fischeer-Schreiber, David O'Neal (Editor). The Shambhala Dictionary of Taoism. Shambhala, 1996.
Another good dictionary of Taoism, but shorter and with fewer entries than the above one.