WordNet (r) 3.0 (2006):

transfer RNA
    n 1: RNA molecules present in the cell (in at least 20
         varieties, each variety capable of combining with a
         specific amino acid) that attach the correct amino acid to
         the protein chain that is being synthesized at the ribosome
         of the cell (according to directions coded in the mRNA)
         [syn: transfer RNA, tRNA, acceptor RNA, soluble
         RNA]