<unk>  is a nail disease that can be a sign of iron-deficiency anemia.<unk>  means literally "spoon nails."   It refers to nails (usually of the hand) which have lost their convexity, becoming flat or even concave in shape.  In a sense,<unk>  is the opposite of nail clubbing. The normal process of change is: brittle nails, straight nails, spoon-shaped nails.
Koilonychia
Platonychia
Onychophosis
Melanonychia
Leukonychia
Xanthelasma
Pachyonychia congenita
Sterculia