Glair is the white of an egg, or a substance like the white of an egg. It can also refer to a kind of adhesive (presumably made from egg white) traditionally used in book binding and gilding.
I love this word because it sounds to me like the kind of sound someone might make while swallowing the white of an egg.
Apparently it comes from a 12th Century Old French word, glaire, meaning the white of an egg, slime or mucus. This in turn comes from the Latin clarus, meaning clear (and also bright and illustrious.)
I don’t know. I still think it sounds like a combination of “gulp” and “bleagh”.