Adenosine is a :- (1) Nitrogenous base (2) Nucleoside

Adenosine is a nitrogenous base made up of adenine and ribose, which is a form of sugar. It forms the core structure of the nucleoside (by adding a phosphate group to it, it forms a nucleotide). As such, it can be used as a biochemical "building block" in the formation of nucleic acids, such as DNA and RNA. In nature, it plays important roles in metabolic processes, including energy production and transfer, cell signaling and tissue repair.