Splinter could be small and stiff (5)
I believe the answer is:
shard
'splinter' is the definition.
(thesaurus)
'small and stiff' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'and' is a charade indicator (letters next to each other).
'stiff' becomes 'hard' (similar in meaning).
's'+'hard'='SHARD'
'could be' is the link.
(Other definitions for shard that I've seen before include "Sharp glass fragment" , "Broken piece (of pottery, glass etc)" , "Sliver of glass, etc" , "Scrap of pottery" , "Sharp piece of glass" .)