Which is correct: I grabbed my wide brimmed hat. Or,
I grabbed my wide brim hat. I think brimmed hat is correct.

I agre with you, but "wide-brimmed" should have a hyphen.

Okay thank you Chris. Bien merci, Wm.

Chris is right about the hyphen, but it is also possible without the hyphen. If the hat has a wide brim, then "wide-brimmed hat" is correct. If it is wide and has a brim, then "wide brimmed hat" works.