PRIMITIVE? reports TRUE if the input word is the name of a built-in Logo command; otherwise, it reports FALSE.

User-defined procedures are not considered primitives; hence PRIMITIVE? reports FALSE when given their names as input.

Compare with DEFINED?, which reports TRUE for both primitives and procedures, and PROCEDURE?, which reports FALSE for primitives and TRUE for  user-defined procedures. All these commands report similarly for both buried and unburied procedures.