Numeral turns it green (7)
I believe the answer is:
integer
'numeral' is the definition.
(thesaurus)
'turns it green' is the wordplay.
'turns' is an anagram indicator.
'it'+'green'='itgreen'
'itgreen' with letters rearranged gives 'INTEGER'.
(Other definitions for integer that I've seen before include "Treeing (anag.)" , "A whole number, not a fraction" , "one or two, perhaps" , "Whole unit" , "Perhaps 60,000" .)