Bone idle at first during a little uprising (5)
I believe the answer is:
tibia
'bone' is the definition.
(tibia is a kind of bone)
'idle at first during a little uprising' is the wordplay.
'at first' suggests taking the first letters.
'during' is an insertion indicator.
'a little' becomes 'abit' (synonyms).
'uprising' says the letters should be written in reverse.
The first letter of 'idle' is 'i'.
'i' going into 'abit' is 'aibit'.
'aibit' back-to-front is 'TIBIA'.
(Other definitions for tibia that I've seen before include "Part of leg of" , "The formal shinbone" , "ancient pipe" , "part of skeleton" , "Bone of the lower leg" .)