Splintered fragments I've fitted in (8)
I believe the answer is:
shivered
'splintered fragments' is the definition.
Although both the answer and definition are past participle verbs, I don't see how they can define each other.
'i've fitted in' is the wordplay.
'fitted' becomes 'shred' (I can't justify this - if you can you should believe this answer much more).
'in' indicates putting letters inside.
'ive' going inside 'shred' is 'SHIVERED'.
Can you help me to learn more?
(Other definitions for shivered that I've seen before include "'Trembled, with cold or fear (8)'" , "Trembled, with cold say" , "showed signs of cold" , "Shook" .)