WHAT IS THE DIFFERENCE BETWEEN PAJAMAS (WITH S) AND PAJAMA?

For my English class students (especially to the sleepy, latecomers, and backroom entities!):
      
        OK. The big difference between "pajamas" --/pah JAH massssssss/ and "pajama" ---/pa JAH maaaaa" is (Are you listening, Artajo?) (Are you in my zone, Paredes?) that: "pajamas" .Noun. "Pajama". Adjective.

       For example: PAJAMAS (noun).  Budods' pajamas are bought from SM mall. The pajamas are made of cotton---or is it poplin? I want to buy some new pairs of pajamas.
                            PAJAMA (adjective).  Blessed invited Jonah and Shamaira to her pajama party. (note: what kind of party? Is it children's party? costume party? No, it is pajama party. Therefore, pajama describes what kind of party. So, it is an adjective!