One writing US city book to miss something on letter once (5,5)
I believe the answer is:
penny black
'something on letter once' is the definition.
(historically type of postage stamp)
'one writing us city book to miss' is the wordplay.
'one writing' becomes 'pen'.
'us city' becomes 'ny' (short for New York).
'book' becomes 'b' (abbreviation for book).
'to miss' becomes 'lack' (lack can mean to be missing).
'pen'+'ny'+'b'+'lack'='PENNY BLACK'
(Other definitions for penny black that I've seen before include "Today one would be unlikely to lick this" , "when without means to send a letter" , "first to get licked" , "World's first adhesive postage stamp, 1840" .)