ˈdēlˈsäldə(r)- noun
Usage: usually capitalized D&A
Etymology: after Otto Diels died 1954 & Kurt Alder died 1958 German chemists
: an addition reaction in which a diene unites with the double or triple bond of an unsaturated compound to form a 6-membered ring (as in tetrahydro-phthalic anhydride)