Word of the Day for Friday, March 6, 2009:
แห่งชาติ /hɛ̀ŋ ˈchâat/ adj. national
Literally "of the nation". This is one of those constructions that isn't hard to understand, but you have to run across it to know the right word. Be sure to note that แห่ง /hɛ̀ŋ/ is pronounced with a short vowel.
หอสมุดแห่งชาติ /hɔ̌ɔ saˈmùt hɛ̀ŋ ˈchâat/ National Library
อุทยานแห่งชาติ /ˈùttháˈyaan hɛ̀ŋ ˈchâat/ National Park
It's mostly found in the names of organizations and such, perhaps better literally translated as "The Nation's X". You wouldn't use แห่งชาติ to say something like, "X is of national importance." In that case you could still use ชาติ, perhaps X มีความสำคัญต่อชาติ or X มีความสำคัญต่อประเทศชาติ.
Also note that ชาติ also occasionally means "national" on its own, as in เพลงชาติ /phleeŋ ˈchâat/ "national anthem".
Bonus vocab: Phrases with ชาติ are very common. Those with the particular sense of "national" include นานาชาติ /naaˈnaa ˈchâat/ "international" (literally "many nations"), and ชาตินิยม /ˈchâat niˈyom/ "nationalist" (literally "favors the nation").