fish skin

noun3

1. •
   The skin of a fish.

   • Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution. — 1974
2. •
   The leather that is made from this skin.
3. •
   (slang, old-fashioned) A dollar bill.

   • I learned quickly that a dollar bill was a fish-skin. — 1936