A looking glass is an object with a surface so reflective that you can see yourself in it — in other words, a mirror. You might check out your reflection in a looking glass before you leave the house in the morning.
Looking glass is a somewhat old-fashioned, literary way to say "mirror." The word glass on its own can mean "mirror" too, coming from a root meaning "to shine." After Lewis Carroll's book "Through the Looking-Glass," was published in 1871, looking glass came to also mean "the opposite of what is normal or expected," like a confusing looking glass world or a mysterious looking glass philosophy.
Close your vocabulary gaps with personalized learning that focuses on teaching the words you need to know.