Material for nails a tinker ordered? (7)
I believe the answer is:
keratin
'material for nails' is the definition.
(I've seen this before)
'a tinker ordered?' is the wordplay.
'ordered?' is an anagram indicator.
'a'+'tinker'='atinker'
'atinker' anagrammed gives 'KERATIN'.
(Other definitions for keratin that I've seen before include "Rate ink (anag) - fibrous protein" , "Protein found in hair and nails" , "Constituent of hair/nails" , "Material in hooves and nails" , "Hair, nails substance" .)