Acrylic is a kind of plastic, fabric, fiber, or paint that's made from acrylic acid. You might knit your mom an acrylic hat if she's allergic to wool.
Anything made of acrylic is synthetic — it's not a natural substance or fiber, but was made in a lab or factory from artificial materials. Acrylic paint is a quick-drying, water-soluble kind of paint that artists often use instead of oil paint or watercolors. The original meaning of acrylic was "containing acryl," from acrolein, the sharp, bitter liquid in onions, rooted in the Latin words acer, "sharp," and olere, "to smell."