To change markedly the appearance or form of:"A thick, fibrous fog had transformed the trees into ghosts and the streetlights into soft, haloed moons"(David Michael Kaplan). To change the nature, function, or condition of; convert: A steam engine transforms heat into mechanical energy. See Synonyms at convert. Mathematics To subject to a transformation. Electricity To subject to the action of a transformer. Genetics To subject (a cell) to transformation.