Sentence:  I pay my personal tribute to Sam Rayburn , stalwart Texan and great American , not only because today he establishes a record of having <WSD>served</WSD> as Speaker of the House of Representatives more than twice as long as Henry Clay , but because of the contributions he has made to the welfare of the people of the Nation during his almost half century of service as a Member of Congress . 
Meaning of the word marked with <WSD> tags:  do duty or hold offices; serve in a specific function