very thin, as thin as a hair
A fishing line made from hair.
The line along one's forehead where hair starts growing.
A very thin line in writing, drawing, or typography.
A very thin fissure.
Elegant, sometimes (derogatory) affected, prissy, or bloodless.
Developed, improved.
Subtle, scrupulous, carefully thought out.
Highly-processed and pure.
Free of dross or alloy.
Dealing in a refined product such as sugar or petroleum.
Elevated and polished.
The refined form of a commodity, as opposed to its raw or generic form.