Oldest or new steel found around the far side of Sheffield (6)
I believe the answer is:
eldest
'oldest' is the definition.
(I've seen this before)
'new steel found around the far side of sheffield' is the wordplay.
'new' indicates an anagram.
'found around' is an insertion indicator.
'the far side of' indicates one should take the final letters.
The last letter of 'sheffield' is 'd'.
'steel' with letters rearranged gives 'elest'.
'elest' enclosing 'd' is 'ELDEST'.
'or' is the link.
(Other definitions for eldest that I've seen before include "Such as Cain, say" , "Most senior of two" , "Most senior of a group" , "Of greatest age" , "Most advanced in years" .)