A trip down memory lane . . .
Snapshot, April 2013, Benita Blocker, age 42 (purple top)
I have always maintained thick eyebrows with the exception of the few times that the estheticians "took half of my eyebrows off!" I had to grow them all the way back in.
I only mention this because your eyebrows can give you some insight about whether your hair is fine, medium, or coarse. Thinner eyebrows may mean that your hair on top of your head is fine to medium, but it has nothing to do with your hair's density on top. You can have fine hair, but have a lot of density.
Thicker eyebrows usually signifies a coarseness to the hair. Also, look at the curl of your eyebrows before you brush them for insight into your curl pattern.