In one direction, following iron, the number is least (6)
I believe the answer is:
fewest
'is least' is the definition.
(I've seen this in another clue)
'in one direction following iron the number' is the wordplay.
I cannot quite understand how this works, but
'direction' could be 'west' (compass direction) and 'west' is located in the answer.
'following' could be 'f' (used when citing page numbers etc) and 'f' is found in the answer.
'number' could be 'e' (e is a kind of number) and 'e' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fewest that I've seen before include "The least number" , "most opposite" , "Least abundant" , "Lowest figure" , "Smallest number" .)