The crossword solution for the term 'shimmer iridescently' is 'opalesce, ' which is an 8-letter word. Opalescence is a phenomenon in which an object appears to have a milky, pearly, or iridescent sheen. It is caused by light diffraction from the microstructures of the material, such as a mineral or a pearl. The term is derived from the Latin opalus, meaning 'precious stone.' Opalescence is often seen in gemstones, such as opal, moonstone, and labradorite, and can also be seen in certain types of glass and plastic.