http://www.envimax.com/engl_enviglos_n.html
N.O.S. 'Not Otherwise Specified'. If a chemical to be transported according to IATA, IMDG or ADR/RID Regulations does not appear in their authorized list, then it is described on the package label under a general heading, for example as alcohol polyethoxylate is not in the authorized list, it would be described as 'Environmentally hazardous substance, liquid, n.o.s. (alcohol polyethoxylate)


http://www.tc.gc.ca/canutec/erg_gmu/en/Glossary.htm
n.o.s. These letters refer to not otherwise specified. The entries which use this description are generic names such as "Corrosive liquid, n.o.s.". This means that the actual chemical name for that corrosive liquid is not listed in the regulations; therefore, a generic name must be used to describe it on shipping papers.


http://ptcl.chem.ox.ac.uk/MSDS/glossary/GLOSSARY.html
NOS is an abbreviation for Not Otherwise Specified.