The Collaborative International Dictionary of English v.0.48:
Iso- \I"so-\, Is- \Is-\ [Gr. 'i`sos equal.]
A prefix or combining form, indicating identity, or equality;
the same numerical value; as in isopod, isomorphous,
(a) (Chem.) Applied to certain compounds having the same
composition but different properties; as in isocyanic.
(b) (Organic Chem.) Applied to compounds of certain isomeric
series in whose structure one carbon atom, at least, is
connected with three other carbon atoms; -- contrasted
with neo- and normal; as in isoparaffine; isopentane.
V.E.R.A. -- Virtual Entity of Relevant Acronyms (September 2014):
International Standards Organisation [International Organization
for Standardization] (org.)