<p><strong>Adjective</strong></p><ul><li>composed of many interconnected parts; compound; composite: a complex highway system.</li><li>characterized by a very complicated or involved arrangement of parts, units, etc.: complex machinery.</li><li>so complicated or intricate as to be hard to understand or deal with: a complex problem.</li><li>(of a word) consisting of two parts, at least one of which is a bound form, as childish, which consists of the word child and the bound form -ish.</li><li>pertaining to or using complex numbers: complex methods; complex vector space.</li></ul><p><strong>Noun</strong></p><ul><li>an intricate or complicated association or assemblage of related things, parts, units, etc.: the entire complex of our educational system; an apartment complex.</li><li>a system of interrelated, emotion-charged ideas, feelings, memories, and impulses that is usually repressed and that gives rise to abnormal or pathological behavior; a fixed idea; an obsessive notion.</li><li>an arbitrary set of elements of a group; a collection of simplexes having specified properties.</li><li>a compound in which independently existing molecules or ions of a nonmetal complexing agent form coordinate bonds with a metal atom or ion.</li><li>an entity composed of molecules in which the constituents maintain much of their chemical identity: receptor-hormone complex, enzyme-substrate complex.</li></ul><p><strong>Verb (used with object)</strong></p><ul><li>to form a complex with.</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>to form a complex.</li></ul>