noun
: any of six isomeric esters CH 3 C 6 H 3 (NCO) 2 of isocyanic acid or a mixture of them ; especially : a liquid isomer made by reaction of tolylenediamine (sense a) and phosgene and used by itself or in a mixture with another meta isomer in making polyurethanes; 4-methyl- meta -phenylene diisocyanate