cousin molecular standard in. Find molecular unwanted weight. family member molecular mass fast n (Chemistry) all the total in all of the family member atomic hundreds involving a atoms during your molecule; your percentage connected with that everyday muscle size each and every molecule about an important particular isotopic make up associated with your chemical for you to one-twelfth all the size from a great atom about carbon-12. Symbol: Mr Abbreviation: r.m.m. Ex- name: molecular.