Adenosine is an example of nucleoside. A nucleoside contains only two basic component of nucleic acid i.e. a pentose sugar and a nitrogeneous base. When adenine [purine base] combines with ribose sugar, adenosine is formed.
A nucleotide contains all the three basic component of nucleic acids i.e. a phosphoric acid group, a pentose sugar and a nitrogeneous base (purines, pyrimidines).