Part of leg somewhat laid back nurses start to ice (5)
I believe the answer is:
tibia
'part of leg' is the definition.
(bone of the leg)
'somewhat laid back nurses start to ice' is the wordplay.
'somewhat' becomes 'a bit' (a bit).
'laid back' shows that the letters should be reversed in order.
'nurses' means one lot of letters goes inside another (nurse can mean to hold onto or harbour).
'start to' indicates taking the first letters.
The first letter of 'ice' is 'i'.
'abit' in reverse letter order is 'tiba'.
'tiba' enclosing 'i' is 'TIBIA'.
(Other definitions for tibia that I've seen before include "Part of leg of" , "The formal shinbone" , "The large shinbone" , "Bone in osso bucco" , "Bone of the lower leg" .)