Definition of "pia"

pia¹

noun
1. (anatomy) The pia mater, the innermost of the meninges that protect the brain and spinal cord.
  Quotations
  One screen in the theatre relays live colour pictures of Harkness and his colleague Tiernan Byrnes's progress, cutting and pushing through first the dura, then the arachnoid and finally the pia, the thin, spider's web-type membranes that cover the brain itself.
  2009 January 25, Denis Campbell, “Kian, 4, needs a miracle. He's in the right place”, in The Observer‎

pia²

noun
uncountable
1. A perennial Polynesian herb whose fleshy tubers yield arrowroot.