Also called acrylic fiber, any of a group of SYNTHETIC TEXTILE FIBERS, such as Arilan and Orlon, that are polymers primarily composed of the acrylonitrile monomer CH2&dbond;CHCN. 2 Also called acrylic resin, any of a group of thermoplastic resins&that are polymers produced from esters of acrylic acid (C3H4O2) or methacrylic acid (C3H6O2). They are used in paints (e.g., Lucite) and plastics (e.g., Plexiglas).