Old measure in fragment of copper? (5)
I believe the answer is:
cubit
'old measure' is the definition.
(I've seen this before)
'fragment of copper?' is the wordplay.
I cannot quite see how this works, but
'fragment' could be 'bit' (bit is a kind of fragment) and 'bit' is found within the answer.
'copper?' could be 'cu' (chemical symbol) and 'cu' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for cubit that I've seen before include "Ancient unit of length based on the length of the forearm" , "Elbow-to-finger measure" , "two such might have been in the yard" , "Measurement based on the length of the forearm" , "Measure of length by which Noah's ark was described" .)