Is a non-compound molecule a chemical substance? The Wikipedia definition of chemical substance states:


  A chemical substance, also known as a pure substance, is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be chemical elements, chemical compounds, ions or alloys.


A molecule made up of the same element (e.g. $\ce{H2}$) is not a compound; however, molecules aren't listed in the final sentence. Is a non-compound molecule a chemical substance?

I believe it is and here's my overall understanding of the terms in this space, and any corrections would be appreciated:
Found that the answer is 'Yes' in the IUPAC Gold Book definition of chemical substance:


  chemical substance
  
  Matter of constant composition best characterized by the entities (molecules, formula units, atoms) it is composed of. Physical properties such as density, refractive index, electric conductivity, melting point etc. characterize the chemical substance.