Digit turns it green (7)
I believe the answer is:
integer
'digit' is the definition.
(thesaurus)
'turns it green' is the wordplay.
'turns' indicates an anagram.
'it'+'green'='itgreen'
'itgreen' is an anagram of 'INTEGER'.
(Other definitions for integer that I've seen before include "Whole unit" , "One for example" , "Treeing (anag.)" , "Gin tree (anag)" , "rational number remains" .)