Sentence:  In a sense , the showdown promised by Mr. Hammarskjold 's sudden and tragic death has been avoided ; no precedents have been set as yet ; structurally , the U.N. is still <WSD>fluid</WSD> , vulnerable to the pressures that its new and enlarged membership are bringing to bear upon it . 
Meaning of the word marked with <WSD> tags:  characteristic of a fluid; capable of flowing and easily changing shape