Blecch is a way of conveying that something is gross or disgusting. People use this word for things that taste icky or look or smell gross, etc. The cs and hs at the end of the worldemphasize that it's pronounced guttural at the back of the throat. For more dramatic effect, it can be written BLEACCCHHH!
adj-
the feeling that you have after washing science goggles in bleach for awhile; something that is very, very white; the way your hands feel after touching bleach a lot in general
My handsfeel so bleachy now >.<; Wow, that person's teeth are very bleachy.