I, odd man, replaced precious stone (7)
I believe the answer is:
diamond
'precious stone' is the definition.
(diamond is a kind of precious stone)
'i odd man replaced' is the wordplay.
'replaced' indicates anagramming the letters.
'i'+'odd'+'man'='ioddman'
'ioddman' with letters rearranged gives 'DIAMOND'.
(Other definitions for diamond that I've seen before include "Something precious" , "The hard stuff" , "Birthstone for April" , "Gem stone" , "rock hard" .)