The term PART OF RNA can be broken down into three crossword solutions: ACID (4 letters), NUCLEIC (7 letters), and RIBO (4 letters). RNA, or ribonucleic ACID, is a type of nucleic ACID that is made up of a chain of nucleotides. The four-letter solution, ACID, refers to the fact that RNA is an ACID. NUCLEIC, the seven-letter solution, refers to the fact that RNA is a type of nucleic ACID, which is a type of organic compound that contains nitrogen and phosphorus. Finally, RIBO, the four-letter solution, is short for ribose, which is a type of sugar found in RNA.