Unexpectedly see pretty old printing plate (10)
I believe the answer is:
stereotype
'printing plate' is the definition.
'unexpectedly see pretty old' is the wordplay.
'unexpectedly' indicates anagramming the letters.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'see'+'pretty'+'o'='seeprettyo'
'seeprettyo' is an anagram of 'STEREOTYPE'.
(Other definitions for stereotype that I've seen before include "received idea?" , "Set form" , "Spring back (in fear)" , "Fixed conventionalised image" , "cast" .)