aw is how English writes this sound. So why au?
vowel-digraphThe au of glaucous is a Latin pair of letters standing for a single English sound. Nothing in that sound points back to either letter.
heard asglawcous
spelledglaucous
saidGLAW-kus
glaucous keeps the Latin au.
English uses aw in its own words, in lawn, dawn and yawn, and au in the ones it borrowed, in cause, autumn and laurel. Glaucous is a borrowing, so it gets au. The rule is about the passport of the word rather than about the sound, which is why you cannot hear your way to it.
The other five