Second difficult piece (5)
I believe the answer is:
shard
'piece' is the definition.
(I know that shard is a type of piece)
'second difficult' is the wordplay.
'second' becomes 's' (common abbreviation).
'difficult' becomes 'hard' (associated in meaning).
's'+'hard'='SHARD'
(Other definitions for shard that I've seen before include "Sharp piece of glass" , "Bit of glass" , "Broken piece (of pottery, glass etc)" , "Broken fragment" , "Piece of broken ceramic - London skyscraper" .)