He could have engineered a file out of a piece of ferrous metal (6)
I believe the answer is:
eiffel
'he could' is the definition.
The definition suggests a singular noun which matches the answer.
'engineered a file out of a piece of ferrous metal' is the wordplay.
'engineered' indicates anagramming the letters (I've seen this in other clues).
'out of' indicates putting letters inside (some letters on the outside of others).
'a piece of' suggests taking the first letters.
'metal' becomes 'e' (E is an example).
The first letter of 'ferrous' is 'f'.
'file' with letters rearranged gives 'eifl'.
'f'+'e'='fe'
'eifl' enclosing 'fe' is 'EIFFEL'.
'have' acts as a link.
Can you help me to learn more?
(Other definitions for eiffel that I've seen before include "Famous tourist tower in Paris" , "& 20 Across Paris landmark" , "Creator of a Paris landmark, built in 1889" , "Great tower of Paris" , "French engineer famed for tower" .)